Accuracy Variations from Magazine Feeding

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Accuracy Variations from Magazine Feeding

Post by Jon Eulette on Fri Oct 27, 2017 10:48 pm


I've been blabbing a lot about first and last round from magazines how they affect groups. I was digging through a box and found an old RR target from my match 45 I shot for many years. I had re-built the pistol for the 3rd time and was testing Federal Match 185gr jswc. Magazine was reloaded after 5th round fed into chamber. 1st & 10th shot were the flyers. Just thought I'd share.
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Re: Accuracy Variations from Magazine Feeding

Post by zanemoseley on Fri Oct 27, 2017 10:54 pm

Geez Jon, you really blew the first and last shot, you should really work on your focus :-)

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Re: Accuracy Variations from Magazine Feeding

Post by Jon Eulette on Fri Oct 27, 2017 10:58 pm

Zane I got my act together on this one just for you Wink
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Re: Accuracy Variations from Magazine Feeding

Post by zanemoseley on Fri Oct 27, 2017 11:29 pm

Jon, do you attribute the shot deviations to high/low magazine spring pressure? I'm not sure I'm good enough yet to observe such variations off hand.

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Re: Accuracy Variations from Magazine Feeding

Post by Jon Eulette on Fri Oct 27, 2017 11:32 pm

Attribute to first round is chambered by hand and last round is probably from less spring pressure.
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Re: Accuracy Variations from Magazine Feeding

Post by Magload on Sat Oct 28, 2017 12:00 am

That is one reason i feed my benchrest AR15 I built single shot using a bob sled  It will shot 1/3 MOA that way but will open the group up when using a 10 round mag.   Don
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Re: Accuracy Variations from Magazine Feeding

Post by Multiracer on Sat Oct 28, 2017 8:25 am

Once the gun goes back into battery isn't every round held by the same components before being struck by the firing pin regardless of when and how it was fed up the ramp ? Each case should be square in the chamber ?

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Re: Accuracy Variations from Magazine Feeding

Post by jglenn21 on Sat Oct 28, 2017 10:25 am

Logic suggests that but ransom rest experience begs to differ.
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Re: Accuracy Variations from Magazine Feeding

Post by Multiracer on Sat Oct 28, 2017 11:01 am

Jon Eulette wrote:Attribute to first round is chambered by hand and last round is probably from less spring pressure.

Wouldn't the last four be getting continually worse until that loss of spring pressure last one ?

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Re: Accuracy Variations from Magazine Feeding

Post by Ed Hall on Sat Oct 28, 2017 12:05 pm

There are many factors involved in the lockup when a round is loaded.  Anybody who has been around 1911s for awhile can probably recall the difference between hearing it "chunk" into battery and "kerr.chunk" into battery.  I personally think (and invite Jon's input) that the difference in the POI is actually due to the gun locking up ever so subtly different due to the round's action on the way in.  How can a magazine affect this?  By its drag on the round as it leaves.  As to the first round vs. the others, it is usually loaded by the dropping of the slide rather than the cycling.  As to the last round, the slide closed while "dragging" on the follower instead of a cartridge.  But, so did the fifth round and it didn't seem to fly.  Jon, could the low left one of the larger group possibly have been the fifth round?

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Re: Accuracy Variations from Magazine Feeding

Post by Jon Eulette on Sat Oct 28, 2017 12:23 pm

Ed I don't remember the 5th shots location. Yes I believe consistency of chambering plays a huge part of grouping from the Ransom rest. Anyone thats tried single loading of cartridges knows first hand Wink
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Re: Accuracy Variations from Magazine Feeding

Post by Magload on Sat Oct 28, 2017 12:26 pm

If we were to shoot the group loading one round at a time would that first round that was out of the group become the center of the group for the next 9 rounds shot the same way?  Or does the round going in and barrel lockup vary each time the first round is loaded?  If drag on the slide causes flyers that that is why my LB wadgun shoots so bad when it starts getting dirty.  It was in the 60s Thursday and the slide was going forward in slow motion with a required thumb push sometimes.  Oiling the rails helped a little.  Don
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Re: Accuracy Variations from Magazine Feeding

Post by jglenn21 on Sat Oct 28, 2017 12:30 pm

no expert like Jon, but I so have quite a bit of time on the RR.. Always thought it was lockup or headspace issue.. maybe one leading to the other.  quit worrying about it after being taught how to get around it.

I always throw the first round away,  then test for group Never letting the gun go to lockback..  that involves loading more than 5 round in a mag...

what really screws up the testing is using different mags on occasion.. you can do the test with a single mag by loading 7 rounds the first time.
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Re: Accuracy Variations from Magazine Feeding

Post by Jon Eulette on Sat Oct 28, 2017 12:33 pm

Accuracy X (Steve Huff) is using 10 rd mags now for RR testing. I haven't tried that yet. I wonder if he lessens the magazine spring tension?
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Re: Accuracy Variations from Magazine Feeding

Post by Multiracer on Sat Oct 28, 2017 1:02 pm

Jon Eulette wrote:Accuracy X (Steve Huff) is using 10 rd mags now for RR testing. I haven't tried that yet. I wonder if he lessens the magazine spring tension?
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Sounds like we need some of these ten round mags for slow fire ?

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Re: Accuracy Variations from Magazine Feeding

Post by Jack H on Sat Oct 28, 2017 1:09 pm

Did you repeat for confirmation?
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Re: Accuracy Variations from Magazine Feeding

Post by LenV on Sat Oct 28, 2017 1:09 pm

All I did was change magazines. Two distinctly different groups. Might want to re-think how often to scope if changing mags.



Last edited by LenV on Sat Oct 28, 2017 6:35 pm; edited 1 time in total (Reason for editing : cause I kant spel)
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Re: Accuracy Variations from Magazine Feeding

Post by Jack H on Sat Oct 28, 2017 1:16 pm

Just hold higher for the first shot and lower for the last shot.   Smile


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Re: Accuracy Variations from Magazine Feeding

Post by Wobbley on Sat Oct 28, 2017 2:25 pm

I seem to recall reading somewhere that this tendency is somehow related to specific magazines.  I.E. some have it, rare ones don’t and some are minimal effect and some are way out there.  Only way to be sure is to test.  And I’m not sure that definitive results can be obtained in a Ransom rest either as slide closing dynamics may affect the position in the inserts.  

So the question often becomes more anecdotal, i.e. the gun shoots better with this magazine than those.

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Re: Accuracy Variations from Magazine Feeding

Post by Magload on Sat Oct 28, 2017 2:53 pm

if drag on the follower is part of the problem then lubing then would lubing the surface of it be a help or even a difference in material the follower was made of.  Maybe this is why I am not a Master i never have cleaned a mag.  Don
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Re: Accuracy Variations from Magazine Feeding

Post by Multiracer on Sat Oct 28, 2017 3:43 pm

Magload wrote:if drag on the follower is part of the problem then lubing then would lubing the surface of it be a help or even a difference in material the follower was made of.  Maybe this is why I am not a Master i never have cleaned a mag.  Don

Delrin would be a nice material for that application. May be a bit thicker for fastening purposes but we only load 5 anyway.. right ?

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Re: Accuracy Variations from Magazine Feeding

Post by Jon Eulette on Sat Oct 28, 2017 4:11 pm

Follower drag is just part of it. Cartridge feeding into feedramp then chamber slightly changes as well.
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Re: Accuracy Variations from Magazine Feeding

Post by LenV on Sat Oct 28, 2017 6:40 pm

Jack H wrote:Just hold higher for the first shot and lower for the last shot.   Smile


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Re: Accuracy Variations from Magazine Feeding

Post by gregbenner on Sun Oct 29, 2017 11:31 am

I am new to RR testing, somewhat shocked to find how much of an art (v science) is involved.  I seem to get an outlier or two quite often with a 10 round string, haven't kept track (so far) of which rounds.  I have been assuming it was the reloads, or perhaps a cold (cooler) barrel.  Never occurred to me it could be the magazine, etc? .  Will have to start paying even more attention:shock:

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Re: Accuracy Variations from Magazine Feeding

Post by Magload on Sun Oct 29, 2017 1:14 pm

I just figured those flyers was because of the wooden plank benches I am stuck with using at the range.  Someone leans on the bench down the line or I get lazy and do it.  Try to do it when i am the only person on the line but by the time I get everything clamped down someone shows up and shoots a rifle off a bag.   Don
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Re: Accuracy Variations from Magazine Feeding

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