adventures with a 1-13 twist slide mount

First topic message reminder :

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

Yes I know gain twist didn't do well. However 1-13 is quite a jump in twist rate from 1-16. Barrel is short so gain will have to be short too. I'm thinking that bullet might strip rifling in that a light power charge will be completely consumed long before bullet leaves the bore. I would think that the initial light load pressure early in ignition will be the same as standard but eventual pressure will not reach pressure needed to get the bullet up to required speed due to lack of power consumption as volume increases when bullet travels down the barrel. Might be interesting to try gain twist so bullet will stabilize to same as 1-16 spin rate with larger powder loads but not strip rifling when it first enters it. That's probably why Black Powder barrels got good results from gain twist. Black powder's burn rate slows as pressure increases but is very fast with low pressure. Maybe a slower burning powder will do the same thing.

Well, so far i have seen nothing unusual in the bore. No lead streaking using conventional lubed and Hi-tek coated bullets.. 

BE seem to be able to manage the lower weight loads much better than Wst. The faster burn rate definitely gives more initial push and that seems to get the slide going, overcoming the initial pressure from the mainspring and the slide weight.  WST seems more even in its pressure and fails with 3.2 gr consistantly.

Just my impressions..  so far i still like the WST feel

Will be interesting to see what group you get at 50 yards. I would check to see how round the hole punched in paper at 50 to see if bullet is stable. On the other hand who cares so long as the group is small.

WST is not good much below 3.7GN that is your problem VN 310 or BE slightly faster powers. 

200gn 3.7 gn WST should be very good with a #11 spring.

finally got a chance to test again today. We left off testing BE with 2.7gr and a 180 Brazos and 2.7gr with a 200 gr Summers bullet

today 2.7 again functioned fine  with the 180 Brazos, but that was the limit for this pistol..2.5 failed to cycle at all.

with the 200 gr Summers we were successful with 2.7 and 2.5gr... 2.5 was right on the limit of functionality as it would function fine but on occasion not lock back.. 2.3 gr would not cycle at all.


So for my pistol and the mods we made , using the 180 gr FB Brazos

3.4 of WST was the limit

2.7 gr of BE was it's limit

for the 200 gr Summers

2.5gr of BE was the limit(but a bit iffy)


final specs on the pistol was the slide cutouts you see in the photos

Eulette Rib

used 10 lb recoil spring( probably like a new 9lb)

19lb main spring with 2 coils cut off..

metalform 7 rd. mags with 6lb mag springs.

.463 crimp on all ammo

last few test were with a Sig 081 STS dot.. Aimpoint T1 copy.


now for the fun part how does it shoot at the long line.

today's target was 3.6 of WST which I would consider my long line load. will test with 3.4 in the future and BE loads also

attached RR target is 2.976" center to center.. that was the width.. easy 10 ring load even with the 2 outliers.

jglenn21 wrote:finally got a chance to test again today. We left off testing BE with 2.7gr and a 180 Brazos and 2.7gr with a 200 gr Summers bullet

today 2.7 again functioned fine  with the 180 Brazos, but that was the limit for this pistol..2.5 failed to cycle at all.

with the 200 gr Summers we were successful with 2.7 and 2.5gr... 2.5 was right on the limit of functionality as it would function fine but on occasion not lock back.. 2.3 gr would not cycle at all.


So for my pistol and the mods we made , using the 180 gr FB Brazos

3.4 of WST was the limit

2.7 gr of BE was it's limit

for the 200 gr Summers

2.5gr of BE was the limit(but a bit iffy)


final specs on the pistol was the slide cutouts you see in the photos

Eulette Rib

used 10 lb recoil spring( probably like a new 9lb)

19lb main spring with 2 coils cut off..

metalform 7 rd. mags with 6lb mag springs.

.463 crimp on all ammo

last few test were with a Sig 081 STS dot.. Aimpoint T1 copy.


now for the fun part how does it shoot at the long line.

today's target was 3.6 of WST which I would consider my long line load. will test with 3.4 in the future and BE loads also

attached RR target is 2.976" center to center.. that was the width.. easy 10 ring load even with the 2 outliers.

Try 3.8 BE or WST on the long line the group should be one hole.

missed the point of the exercise.. find the lowest softest loads that will still shoot good scores.. we'll see how the rest of low loads do at the long line.

Jim,
Would be interesting to know what your red dot and mount (if any) weigh.  If anyone wants to duplicate this it will make a difference how much total slide weight is being cycled.  Great experiment!

Thanks Don,

Will try and get all those weights tomorrow. I have several T1 copies i  can weigh.  Also have an identical slide to the one i cut up, so we can see how much weight we eliminated.

It's not just weight but lug and pin friction, slde friction, firing pin stop contour, phase f the moon, etc so your results will vary.

the following weights were done on a USPS certified scale..  

new bare slide...13.2 oz.
cut up slide.........12.6 oz.
Eulette rail and 4 screws  2.0 oz.

Std. GI firing pin, FP spring, EGW practical extractor and slide stop.. 0.6 oz.


Dots:

Sig STS-081 with graphite tubes....   4.8 oz
Konus sight pro atomic with tubes.....4.6oz( same style as Sig)
Primary arms MD-RBG II  ................4.8oz


Probably not the lightest slide out there.. this one was was a bare slide off ebay for around $100 last year. actually very nice quality.. had interesting upper lugs cuts..

pictures of my lower lugs and side shot of my firing pin stop angle
 

Thanks Jim.  Good data.

Just a quick update of ransom testing with BE. We shot 2.9 and 2.7 with the 180 Brazos along with 2.7 amd 2.5 with 200gr Summers. All of them performed horribly. A ton of vertical stringing on each 10 rounds.. as a side note, 2.5 with the 200 functioned but never moved the ransom rest.  Rounds fell out of the slide.. my partner for the day enjoyed watching the slugs  go down range...

After checking the pistol i found a touch of barrel bump on the lower lugs and have since fixed that. I don't believe that is the full reason for the vertical issues.  At some point you reach the lowest load that will function,  but more than likely you have introduced poor/inconsistent lockup issues..thus the vertical stringing. 

Having reached the  bottom of functional loads I'm going to work my way back up looking for the 1st load that will give acceptable accuracy at 50yds. I will also test some at 25 looking for a short line load. I commonly use two loads for the LL and the SL.    Using WST  i pretty much settled on 3.6 and 3.4 for the two lines.  

I'm also going to install a new 10lb recoil spring to see if that helps lockup.  The one currently in the gun is quite used and probably close to 9lbs.  

Back to the loading bench

I found when testing really low powder charges that lead clogged the barrel and destroyed accuracy within a few shots. I can't find my notes from the time but I think I was down around 3gr Bullseye with 185/200gr lead bullets. I assumed it was insufficient pressure to seal the bullet against the barrel and the flame cut/melted lead on the side of the bullet, leaving it behind in the barrel.

Steve, I was running the Hi-tek coated bullets so not leading at all.

well I finally got around to testing some rounds with slightly higher loads of BE at the long line. the the targets were all 180 FB Brazos bullets winchester cases and primers. nothing special other than checking the bases of the bullet when loading them on my 750.. .463 crimp as  usual with this barrel testing

targets show 3.1 , 3.3 and 3.5 of BE.. you can see the slow improvement.

pistol definitely likes BE at the long line with reduced loads..WST performed fine at the short line with 3.3 to 3.6 but was poor in comparison to BE at the long line.. WST will perform when you get close to 4.0 of BE but that defeats the whole idea of reduced recoil loads using a 1-13 barrel..Overall I think the KKM 13 twist barrels show a lot of promise stabilizing slower bullets.. 10 and 12 twist barrels may yet yield better results but that's a future test coming soon I hope..