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adventures with a 1-13 twist slide mount

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Post by jglenn21 5/27/2021, 3:20 pm

as somewhat of a followup to Jon's Thread on a KKM  1-13 twist Frame mount, I decided to build a 1-13 KKM wad gun using the typical slide mount. Specs for the gun follow:

1-13 twist KKM barrel

10 lb ISMI recoil spring

modified slide to lighten it up( see pictures). copied from a slide Jon did a while back that he showed me..

7 round Metalform Magazine...round follower and a wolff 6lb mag spring

Eulette Precision rail(lightest around)

aimpoint T1 copy with graphite tubes

All loads used Win LPP


This is a new build 

I'm a big fan of WST at the short line due to it's recoil impulse so my initial testing used it. My standard load for a flat base 180 Brazos or Summers bullet is 4.0 of WST..  For the testing I started with 3.8, 3.6 and 3.4 of WST to see where I stood. in my initial test 3.8 functioned fine but 3.6 did not cycle the slide fully. I then fired around 100 rounds of 4.0 to let the pistol settle in as it was pretty tight.

before my second day of test it dawned on me that my normal crimp for lead bullets is .468 so I decided to take that down to .465 for todays' test.. this time out 3.6 functioned perfectly as did 3.4..   no test targets as I was simply checking for functionality.. my indoor range is limited to 25 yards so no long line tests but all rounds seemed on call.  will eventually get the RR out and see how they run at the long line.

I will also develop some light BE loads just to give a base line with that powder.. I did have some 3.5 BE loads using a 200 GR. H&G 68 bullet laying around that functioned perfectly and actually were a bit snappy

1st picture is of my slide modification.
2nd picture is the rail set on top covering all the cuts.
3rd is the completed pistol

I firmly think the 13 twist is worth a look if you want reduced recoil..

many thanks to Jon for his help and yes I have stayed in a Holiday Inn before
adventures with a 1-13 twist slide mount 13slid13
adventures with a 1-13 twist slide mount 13slid12
adventures with a 1-13 twist slide mount 13pist10
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Post by jglenn21 6/3/2021, 7:27 am

Test with 3.2 of WST failed to fully eject, so for now 3.4 seems to be  the minimum of WST that works.with the 180s.

BE testing will be next using both 180 and 200 gr lead..

Eventually i may cut on the slide a bit more.
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Post by bruce martindale 6/3/2021, 1:58 pm

Crimp is worth powder. I see about 50 fps gain going from 0.470 to 463

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Post by jglenn21 6/3/2021, 3:51 pm

I did go down to 463 on the 3.2 loads. Still no joy. Some things left to try but on to testing BE next.
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Post by SmokinNJokin 6/4/2021, 7:00 pm

Just curious, what weight is your mainspring and what does your firing pin stop look like? 

My ball gun (yeah I know, lighter slide) cycles as low 2.7 WST with 180gr swcfb, .465 crimp and 9lb recoil spring. I don't use the load, because it sprayed my arm with unburned powder particles and accuracy wasn't great with a 1:16 barrel but it cycled fine and locked the slide. I have a very rounded firing pin stop and lighter mainspring that were a big help cycling light loads.

Your results may vary of course because of the weight of the dot. My go-to short line load for lead is 2.7 gr vectan ba10 (similar to bullseye) and a 180 swcfb. Feels like a 38. And at the time when I stocked up, ba10 was the cheapest powder, 180s were the cheapest bullet... you may see a pattern. I can guilt free blast thousands of short line rounds a week in practice.

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Post by jglenn21 6/4/2021, 9:22 pm

Currently has a fairly standard curve on my EGW FP stop and a 19lb mainspring which is my norm. 10lb recoil spring.

A 9lb recoil spring, 17lb mainspring and additional slide work are all possibilities. Not many rounds through the gun at this point so the unlocking is very tight. Accuracy at the long line verses recoil is the compromise we'll end up with.
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Post by jglenn21 6/10/2021, 2:41 pm

Not having a 17lbs mainspring on hand, I simply cutoff 2 coils from a 19lb spring and tested a bit today, still with my 10lb recoil spring. I had no failures to fire with the new mainspring through 50 some odd rounds.

3.2 WST and a 180gr again failed to eject even though the pistol has noticeably less effort to unlock.
3.4 of WST continued to run fine..

Initial testing with BE:   .463 crimp

3.5, 3.3 and 3.1gr. with  180 Brazos all functioned perfectly including locking the slide back.

3.1 and 2.9 gr with a 200 H&G 200gr both functioned perfectly.

I'll keep lowering the loads with both 180 and 200 gr bullets..

I feel  2.9 of BE will work easily with the 180 just based on the recoil impulse of 3.1 today. we'll start there for the next test..

Recoil impulse between WST and BE is markedly different..3.4 of WST is quite mild while 3.1 of BE still has a bit of snap to it...


Last edited by jglenn21 on 6/10/2021, 4:21 pm; edited 1 time in total
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Post by spursnguns 6/10/2021, 4:01 pm

jglenn21,

I had to read this thread twice.  Do you have anything quantitative regarding accuracy?

Thanks.

Jim
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Post by jglenn21 6/10/2021, 4:26 pm

nothing yet at the long line. all testing has been at my indoor range which is 25 yards..everything there has been on call. will eventually be testing at 50 with a RR. will test both the lowest load that functions against something a bit higher with both powders hopefully.
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Post by spursnguns Yesterday at 10:11 pm

Hello jglenn21,

That's what makes life a horse race.  I'm not sure that I would have approached the process the same way but "you keep doing you".  Good luck.

Jim
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Post by jglenn21 Today at 7:00 am

Thanks, whole project is to simply see what the practical limits are for a slide mounted dot gun using powder puff loads verses a frame mount that Jon is working on.. honestly think we can get close but not quite what a frame mount can do..  hopefully generate some interest from others who work on their own guns
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Post by Dcforman Today at 7:55 am

I, for one, am interested, as Jon is (hopefully) finishing up my 1:13 slide mount shortly. Saving me some load development!

Dave

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Post by spursnguns Today at 11:53 am

Hello all,

I guess it all comes down to....what are the conditions where accuracy trumps recoil or vice versa?....

e. g. you have two different loads:
   Same accuracy but one has lower recoil - no brainer for me
   One loses 0.5" in accuracy but has lower recoil - personal choice
   One loses 1.5" in accuracy but has lower recoil - personal choice
   Etcetera
   One loses 6.0" in accuracy but has lower recoil - no brainer for me

Nonetheless, I remain interested in your results.

Jim
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Post by jglenn21 Today at 4:07 pm

Dave be interesting to see how your testing compares to my slide mount. Every gun is a bit different...will hopefully.het more.testing done this week and probably shoot it next week in a match as my 45..

 I pretty much have always used a lighter load for the short line and a heavier load for the LL so i may end up with a heavier load for the LL and a very mild load that has acceptable SL accuracy..

One thing i have noticed so far is very small changes with slide weight really show up with these marginal loads.  I swapped dots last week and the lighter loads failed to function as they had the week previous. Both dots were T1 copies and appear very close to one another but the one was a tad heavier.. swapped back to the Primary Arms dot and continued to test. Heavier dot was a Sig..
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Post by Dcforman Today at 4:18 pm

Yeah, it might be different, but what you come up with will be a good starting point. Mine will have a Kodiak rail with an H1, trying to keep it light. I typically use one load for both lines for simplicity's sake.

Dave

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