How low is too low?

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How low is too low?

Post by Dcforman on Sun Jan 14, 2018 3:54 pm

How light is too light for loads? How do you know when you've hit a load that's too Light? Accuracy drops off? Is there any risk outside of simply failing to cycle the gun?

I know I'm asking a lot of questions. I swear im searching the forum before I post!

Thanks all!

Dave

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Re: How low is too low?

Post by Jon Eulette on Sun Jan 14, 2018 4:03 pm

For 25 yds if it cycles and a good pistol it will hold X. At 50 yds you need more velocity to group. Also if recoil spring weight gets too light groups will open it.
I use 3.3-3 4gr BE for 25 yds. For 50 yds I use 3.7-4.0 BE.
With lighter charges some guns will need 200 gr lswc to cycle. 185 won't build enough pressure because it doesn't seat as deeply as a 200 so more case volume.
Jon
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Re: How low is too low?

Post by 10sandxs on Sun Jan 14, 2018 4:43 pm

I wondered the same thing a few months ago. I was down to 2.0 (two) grains of vectan BA10 and the gun functioned fine with little, if any loss of accuracy. 

Only issue was below 2.7 gr, powder burned like ground up lignite coal...  after 100 rounds the fouling looked like 1000 of normal BE loads.

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Re: How low is too low?

Post by MarkOue on Sun Jan 14, 2018 6:54 pm

I add a couple to few tenths of a grain of powder for the 50 yard loads.  For me that keeps both the 25 and 50 yard line zero the same.  

Also, with an optic mounted on the slide I have to increase the powder charge by a few tenths to a half grain.  

Otherwise, like Jon stated, run enough to ensure proper functioning and maybe add a couple tenths of a grain for insurance.

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Re: How low is too low?

Post by S148 on Sun Jan 14, 2018 10:15 pm

Jon Eulette wrote:
With lighter charges some guns will need 200 gr lswc to cycle. 185 won't build enough pressure because it doesn't seat as deeply as a 200 so more case volume.
Jon

Pressure and case volume? This is confusing. 

With the same powder charge, lighter bullets produce less recoil force. Chamber pressure and case volume, as variables, are irrelevant. What matters is recoil force being balanced with recoil spring weight, and this should not be confused with secondary features/variables.

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Re: How low is too low?

Post by zanemoseley on Sun Jan 14, 2018 10:39 pm

S148, Jon is absolutely correct. The pistol needs to generate enough pressure to cycle properly. Pressure generates recoil. There are a lot of factors that contribute to load pressure:
- charge weight
- powder burn rate
- case capacity
- bullet weight
- bullet diameter
- bullet hardness
- bearing surface length

Other factors like slide weight and dot/ring weight on slide mount guns need to be overcome to cycle. How tight the barrel is fit also affects function and amount of pressure needed to cycle.

Light bullseye loads are a balancing act. We all want extreme reliability but also want the minimum recoil possible, the trick is getting it all balanced out.

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Re: How low is too low?

Post by Jon Eulette on Sun Jan 14, 2018 10:52 pm

The 200gr lswc will seat deeper into the case which results in less case volume than when a 185 gr lswc is seated. As a result the pressure is higher. It is not noticeable until you start shooting reduced powder charges. When I shoot 3.3-3.4 gr charges of BE there is a large difference in felt shot and recoil. I personally do not think 15 gr of bullet weight makes much difference, but I do believe case volume when loaded with the different bullets makes a larger difference. I'm not a ballistician, I have a decent understanding of physics from my engineering curriculum, but I have many years of experience shooting reduced loads at a high level of performance. So if I'm wrong I would admit it if proven otherwise.
Shot from the same pistol with same recoil spring and the same barrel.....same same same....there is a distinct difference. I work on many pistols. I have worked on majority of the old school smiths guns; Clark, Giles, Shockey, Best, Aikman, Nygord, etc. I always shoot them alongside one of my own pistols. They kick like hell with the same exact load. Shooting is relative. It's relative to what you want to compare it too. A poorly built new pistol will behave like the older pistols. I also don't expect other shooters to 'feel' what I can feel when they shoot. Poor barrel fit or old barrels with shimmed upper lugs have more felt recoil than a pistol with deeper upper lugs and longer bearing surface on the bottom lugs. The camming action of the barrel unlocking has a great deal of effect on felt recoil. So depending on how 'hard' a shooter can hold and how the pistol was built also determines whether light charges are going to function in their pistol. It's not for everybody.
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Re: How low is too low?

Post by S148 on Mon Jan 15, 2018 12:10 am

Let’s do the math and see how much an effect bullet weight has on recoil. The issue is 185 grain versus 200 grain lead bullets in the 45 ACP.

What’s required for calculating recoil force is bullet weight, velocity and gun weight.

Velocity and pressure estimations were done in Quickload (version 3.8.0.2). Velocity calculated for a 5” barrel.  Recoil force was calculated for 2.5 pound gun.

Bullet length is required for the last calculation of pushing the 185 grain bullet deeper in the case to take up the same space as the 200 grain bullet.

Bullet lengths are from Cast 185 and 200 grain SWC bullet of the same shape (bevel base) that I had on hand. Their nose shape looked pretty similar. 

200 cast. bullet length 0.650”
185 cast bullet length 0.615”

Calculation parameters:

OAL = 1.250
Bullseye 3.3 gr

200 cast:
chamber pressure: = 6,977
fps = 631
muzzle pressure = 1449
recoil force = 2.12 ft lbs

185 cast:
chamber pressure = 5,971
fps = 621
muzzle pressure = 1391
recoil force = 1.77 ft lbs

Difference in recoil force  (1.77 - 2.12) / 1.77 = -0.1977

The 200 grain bullet produces 20% more recoil force.


Lets seat the 185 grain bullet deeper to take up the same space as the 3200 grain bullet and see what we get. If filling the space is all that’s required, the deep seated 185 grain bullet should produce as much recoil as the 200 grain bullet.

185 cast at 1.215” OAL
chamber pressure = 6614
fps = 639
muzzle pressure = 1392
recoil force = 1.87 ft lbs

The 185 grain bullet is now producing more speed than the 200 grain bullet.

difference in recoil force  (1.87 - 2.12) / 1.87 = -0.1336


The 200 grain bullet still produces 13% more recoil force.

My conclusion. Bullet weight is the largest factor in this comparison of recoil force. 

Chamber pressure in itself is not a significant variable because one can change powders and produce less chamber pressure but more velocity.
  
Volume of space is important but to a limited degree, because using a different powder can change the available space, such that it becomes less of a variable in this calculation.

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Re: How low is too low?

Post by Jon Eulette on Mon Jan 15, 2018 1:37 am

S148
Can you give me an equivalent powder charge for the 185 to equal the 200 with 3.4gr BE?
I'd like to increase 185 powder charge to see if it 'feels' similar to the 200 @ 3.4 gr and see if it will function my pistol.
Obviously basing this on your math calcs.
Jon
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Re: How low is too low?

Post by S148 on Mon Jan 15, 2018 1:44 am

zanemoseley wrote:S148, Jon is absolutely correct. The pistol needs to generate enough pressure to cycle properly. Pressure generates recoil. There are a lot of factors that contribute to load pressure:
- charge weight
- powder burn rate
- case capacity
- bullet weight
- bullet diameter
- bullet hardness
- bearing surface length

Other factors like slide weight and dot/ring weight on slide mount guns need to be overcome to cycle. How tight the barrel is fit also affects function and amount of pressure needed to cycle.

Light bullseye loads are a balancing act. We all want extreme reliability but also want the minimum recoil possible, the trick is getting it all balanced out.

People should avoid thinking or saying that pressure is the key element in recoil or reliable functioning.  It's terribly misleading and could lead one to come to the wrong conclusion.  Recoil force is a function of: bullet weight, velocity and gas pressure at the muzzle.  And gun weight, of course. https://en.wikipedia.org/wiki/Recoil

The weight of the powder is important because it, along the bullet speed, helps to calculate the gas pressure and gas speed at the muzzle. The various formulas that calculate recoil force vary in what value they use for the gas speed since there is little agreement.  If you look at the recoil calculator at this site: http://kwk.us/recoil.html  you'll see some of the various multiplication factors used for gas speed.

Peak chamber pressure does not predict gas pressure at the muzzle. http://www.shootingtimes.com/ballistics/compensators-pressure-gas/ Fast powders can produce high peak chamber pressure but low muzzle gas pressure because they usually require less charge weight for the same velocity as slower powders. The greater weight of a slower powder will produce more recoil force even though it pushes the same bullet to the same speed as a fast powder because of the conservation of mass effect, explained at the wikipedia link.  This effect has been well documented. http://www.shootingtimes.com/ballistics/measure-relative-handgun-recoil/

So the whole 'pressure is required to cycle the gun' thing isn't accurate. And what do people mean when they say pressure?  Some don't know. Bullet weight and speed are the big players, especially for handgun rounds, and gunpowder weight makes its contribution via the mass and speed of gas ejecta.

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Re: How low is too low?

Post by S148 on Mon Jan 15, 2018 2:04 am

Jon Eulette wrote:S148
Can you give me an equivalent powder charge for the 185 to equal the 200 with 3.4gr BE?
I'd like to increase 185 powder charge to see if it 'feels' similar to the 200 @ 3.4 gr and see if it will function my pistol.
Obviously basing this on your math calcs.
Jon



Sure, Jon.    It looks like 3.8 gr BE will be the best match. 

Here are the calculations via Quickload.  Both loaded to 1.250 OAL. 

200 grain, 3.4 gr BE, velocity = 647 fps, recoil = 2.23 ft lbs.    power factor 129

185 grain, 3.7 gr BE, velocity = 684 fps, recoil = 2.16 ft lbs.

185 grain, 3.8 gr BE, velocity = 700 fps, recoil = 2.26 ft lbs.    power factor 130

They are likely to feel a little different. The 185s will probably feel a little snappy compared to the 200s because the 185s will be accelerating faster to reach their higher speed.  There is some discussion of this at this link: http://www.shootingtimes.com/reloading/power-factor-recoil-bullet-weight-gives-edge/    I included the power factor since that is consistent with one of the things discussed at the article I posted the link to.

Let us know how it goes.

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Re: How low is too low?

Post by mspingeld on Mon Jan 15, 2018 7:41 am

So how does crimp affect these velocity/recoil/power factor calculations?

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Re: How low is too low?

Post by zanemoseley on Mon Jan 15, 2018 7:59 am

S148, can I guess that your background is in precision long range rifle shooting?? I say this because your calculations reflect what a lot of rifle shooters do to maintain safe loads while cheating the upper limits of the cartridges, we're talking about the exact opposite scenario here.

Jon and I are trying to give you some real world advice here backed by a lot of experience, a lot more years in Jon's case. I have real world examples that have proven some of the factors I listed, I've had 2 different 185 grain bullets take drastically different powder charges to cycle the same gun, the difference between them primarily being bearing surface, Magnus #801 versus H&G 68.

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Re: How low is too low?

Post by USSR on Mon Jan 15, 2018 8:35 am

Jon Eulette wrote:For 25 yds if it cycles and a good pistol it will hold X. At 50 yds you need more velocity to group. Also if recoil spring weight gets too light groups will open it.
I use 3.3-3 4gr BE for 25 yds. For 50 yds I use 3.7-4.0 BE.
With lighter charges some guns will need 200 gr lswc to cycle. 185 won't build enough pressure because it doesn't seat as deeply as a 200 so more case volume.
Jon

Interesting discussion.   In my case, my 185gr lswc is a hollowpoint version of the H&G #68 200gr bullet, so same bullet dimensions as when I cast it as a 200gr lswc.   So, since the 2 bullets are seated to the same depth and case volume is identical, and the only difference is bullet weight, it seems that the difference in charge weight between the 185gr and 200gr bullets would be a little less than described above.   Yes?

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Re: How low is too low?

Post by Wobbley on Mon Jan 15, 2018 10:39 am

One thing to remember here. It isn’t pressure ot recoil energy that cycles the gun. It is recoil impulse. The impulse is the bullet mass times the velocity. The recoiling mass of the pistol (slide, sights and barrel) have the same impulse. The hammer spring and it’s mechanism retard the recoiling mass and can be accounted for by adding an additional mass to the slide.

Also, slow motion videos indicate that the biggest contributor to pistol motion after the shot is the impact of the slide at the full rearward stop. Depending on the load and to some extent the setup of the pistol, this can be quite violent.

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Re: How low is too low?

Post by S148 on Mon Jan 15, 2018 12:07 pm

mspingeld wrote:So how does crimp affect these velocity/recoil/power factor calculations?


I don't know.

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Re: How low is too low?

Post by S148 on Mon Jan 15, 2018 12:25 pm

zanemoseley wrote:S148, can I guess that your background is in precision long range rifle shooting??  Your assumption is wrong.  I say this because your calculations reflect what a lot of rifle shooters do to maintain safe loads while cheating the upper limits of the cartridges, we're talking about the exact opposite scenario here.

Jon and I are trying to give you some real world advice here backed by a lot of experience, a lot more years in Jon's case. I have real world examples that have proven some of the factors I listed, I've had 2 different 185 grain bullets take drastically different powder charges to cycle the same gun, the difference between them primarily being bearing surface, Magnus #801 versus H&G 68.

With the two bullets you describe, they have different amounts inside the case (short nose versus long nose, but bullets of the same weight). Here, depth in the case matters. The button nose magnus 801, seated deeper, will raise pressure and most importantly - velocity. Seating the same bullet deeper has this effect. (I have data for this.) You'd get the same effect by seating the H&G to the same depth in the case as #801. This is why bullet length matters. This procedure would also test the "bearing surface" argument.

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Re: How low is too low?

Post by xmastershooter on Mon Jan 15, 2018 12:48 pm

I've been experimenting with different loads for several months now. 

Here are some of my practical findings:
I have reduced my long line load from 4.0 gr BE to 3.8 gr BE with the 185 gr. HPSWC using a 10 lb recoil spring and without loss of accuracy.

The fun began with the short line loads.  The felt recoil with the 200 gr was never the same as the 185 gr bullet no matter what BE charge I used, starting with a low of 3.4 gr BE.  The 3.4 gr BE and the 200 gr bullet always functioned in my pistol even in colder temperatures.  I'm referring to California cold and not Mid-West or East Coast cold.  I needed 3.7 gr BE for the 185 gr bullet to function all the time especially in colder temperatures.  In warmer temperatures, 3.6 and 3.5 gr will work.

The felt recoil with the 3.4 gr BE and the 200 gr bullet was a shorter snap and recovery of the red dot back to the bull.  The lesser  recoil with this load at times made me more complacent as I tried to take the next shot, with the tendency of taking more time.

The 3.7 gr BE with the 185 gr bullet had a little more recoil so the pistol went further out after each shot and I had to concentrate more to get the red dot back to the bull.

Going with the 3.8 gr BE and the 185 gr bullet in the short line, the slight increased recoil could be "our friend."  After the shot, my arm seem to snap back into position so that the red dot bounced back into the black quicker without much effort.  My hold tend to be better and this led to the next trigger release more automatically.

I believe I found my loads that are comfortable for me and my pistol.  No more testing needed.  I don't put any value with data.  Data isn't what shoots the gun.  It's the shooter.  I'm sure my post may make sense to some and a lot of nonsense to others.

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Re: How low is too low?

Post by Jon Eulette on Mon Jan 15, 2018 3:52 pm

3.8 gr BE with 185 lswc is a 50 yd load in my pistol. Kicks a great deal more than my 3.4 gr BE 200 lswc. I find it takes more effort to recover on the short line. Lately I've been shooting heavier slide/scope pistols. They require the 200gr to function. On my lighter slide/scope pistols I can run 185 with 3.3-3.4 with no issues. I can barely feel a difference between the two bullets in recoil.
Crimp makes a huge difference in getting lighter charges to cycle the pistol. I shot .467-.469 for years and found I had to drop to .465 to get pressure up to cycle the gun. I don't chronograph.....I just shoot. Maybe someday I'll cross that line. But I know what works for me from success and failure.
Thanks for the data.
Jon
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Re: How low is too low?

Post by lablover on Tue Jan 16, 2018 8:49 pm

I wonder how low one could go with a 190 gr bullet and slide mounted dot?

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Re: How low is too low?

Post by USSR on Tue Jan 16, 2018 9:03 pm

lablover wrote:I wonder how low one could go with a 190 gr bullet and slide mounted dot?

I'll tell you when the weather breaks with my Roddy Toyota wad gun.   My H&G 68 clone mould casts hollowpoints at 184gr and solids at 190gr.

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Re: How low is too low?

Post by xmastershooter on Tue Jan 16, 2018 10:30 pm

Jon Eulette wrote:3.8 gr BE with 185 lswc is a 50 yd load in my pistol. Kicks a great deal more than my 3.4 gr BE 200 lswc. I find it takes more effort to recover on the short line.
I'm curious how much difference in the felt recoil with my lesser crimp and seating.  I crimp .469, and seat .926 to .928 from the shoulder.  Your crimp is .463, and seat .922 if I recalled correctly. I'm hesitant to change my die settings because it takes quite a bit of effort to readjust back and forth.  If you're coming to the state match this year, perhaps we can swap some rounds to compare.

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Re: How low is too low?

Post by Jon Eulette on Tue Jan 16, 2018 11:28 pm

Norman,
You won't see any difference until temperature drops down into the 40's. Then the crimp really makes a difference. I've used various OAL's and crimps and they all perform about the same. But when temperature goes down you can feel the slide slow down and the brass just clears the ejection port.
If I come up I'll bring you some.
Jon
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Re: How low is too low?

Post by SNaymola on Wed Jan 17, 2018 5:55 pm

I wonder how hard it would be to instrument a ransom rest or similar test rig to measure recoil impulse?
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Re: How low is too low?

Post by S148 on Wed Jan 17, 2018 6:02 pm

SNaymola wrote:I wonder how hard it would be to instrument a ransom rest or similar test rig to measure recoil impulse?
Stan

You might have to redesign it significantly. The rocker arm pivots upward, but the recoil force is aligned with the barrel and slide which is force directed to the rear along that axis. At present you can measure how far the rocker moves - upward around the pivot point - and that probably correlates reasonably well with the mathematically calculated recoil force.

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Re: How low is too low?

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