Gas Cutting/Leading

[4060MAY]

We finally made a bullet catching box 8' long filled with sawdust in plastic bags with cardboard spacers. Trying to figure out why the Uberti 38-55 is leading.
We tested 2 loads 16/2400 and 26/4895 patched 300gr bullet .374 dia. 13BHN, two wraps .002 onion skin, bore dia is .375, groove dia is .381.
Patch is not twisted on the bottom just laid over not to the center.
We didn't Chrono the loads, but should be around 1500fps maybe faster.
the bullet goes thru to the end of the trap 8'.
looking at the bullets there is gas cutting on the one side about half way up the bullet, in two to four places, pictures as soon as I can, wasn't smart enough to do it yesterday.
The 4895 showed many dents on the base and the base was cupped on both bullets

Any suggestions how to stop the gas cutting? do we have to use the twisted method and cutoff with dikes? my 38-50 with Black powder absolutely does not lead with PP, but a 40-65 Sharps does the same thing the Uberti does, using 18/4759 400gr bullet.

[Slowpoke]

No first hand experience with that caliber, but I would guess you need a bigger boolit with smokeless.
good luck

[longbow]

If you are getting gas cutting it sounds like the patch is either too thin or is tearing. Though from the dimensions you give the boolit is about right for smokeless loads and 0.008" patch should put you just over groove diameter which should work.

Did you recover any patches? They can tell a tale. If they are burned or torn you should be able to tell.

Did you crimp? Crimping can cause patch tearing.

Possibly the throat or rifling has sharp edges that are tearing the paper.

You might try a little thicker paper with high linen or cotton content and see if it helps. Maybe a little tougher and maybe would seal better. You might have to size after patching though. I have shot way over sized PP boolits in my .308 at up to 0.314" and they shot well.

The advice I have been given is about bore size boolit for smokeless load and patch to groove diameter or a little over. My .44 isn't picky but my .303 British follows that rule. With BP the tendency is to have the patched boolit just over bore diameter.

Another thought too is my .303 performed much better with knurled boolits and I am not sure whether it is the slight diameter increase, better grip of paper to rough lead or a combination. You could try rolling the boolits under a coarse file to roughen the surface a bit before patching. It is easy to do and may help.

Longbow

[4060MAY]

no crimp, no throat, rifling starts at the end of the chamber, from chamber to rifling looks like about 60* angle
no patch material to be found any bigger than 1/4" long X the width of the rifling

Our next attempt will be with my bullet @.360 with three wraps of paper. might even back the load down a bit.

I'll have some pictures tomorrow

[45 2.1]

I shoot a cast 250 gr. smooth sided flat based slug in this caliber. I size to 0.372" in a Lee push thru and knurl the smooth side with a heavy tooth file by rolling it. I patch with 9 lb. onionskin, twist and nip the tail while still damp then roll and press the nib fairly flat on the base twisting it in the direction it was already twisted. No problems with the patch or loading. I've recovered over 60 of them in expansion tests. No problem with accuracy or with the powder imprinting into the base lead either. Bases look awfull with total coverage of powder imprints. No torn patches or gas cutting. I've ran these through the 375 Win, 375 H&H and the 38-55. I would twist and nip close, then twist it into the cupped brass where it was smooth and give that a try. Make shure the patch is over the ogive so the land won't peel it when fired. SR 4759 works very well in this caliber.

[longbow]

You might be better to use two wraps of slightly thicker paper - maybe 0.003" to 0.004" - than 3 wraps. I'm not sure that 3 wraps is bad but I tried it unsuccessfully. Maybe too much room to squirm a bit?

I'm not sure how thick 45 2.1's 9 lb. onion skin is but you can buy paper is a variety of thickness from about 0.002" to 0.005" so fit can be tailored as required. Some people also size after patching but I have shot everything as patched.

Anyway, trying thicker patch one way or another is probably a good thing to do.

I'm certainly no expert here and have limited experience with paper patching but it has worked well for me and normally I find substantial pieces of paper patch after shooting. I always pick up some pieces and take a look for burning. Usually the outer wrap shows pretty good rifling impression and the inner wrap shows the knurling impression if things are going well and if not the patch is either shredded or shows burning.

Longbow

[oso]

What are you using to lube the paper?

[Buckshot]

[QUOTE=4060MAY;299372]there is gas cutting on the one side about half way up the bullet, in two to four places. Any suggestions how to stop the gas cutting? QUOTE]

................Just want to be sure I'm reading this right? Do you mean that the gas cutting starts halfway up the boolit and continues to the ogive? In order for there to be gas cutting the gas has to be able to pass the boolit to reach the low pressure area ahead of it. Evidence of it may show that it changed direction, ie: circled the boolit in a lube groove then returned to a forward path to escape, but escape it must to cut the boolit.

The only way for this to happen is that your boolit/patch combination is too small, or both are being damaged somehow, as the slug is released by the case and the slug's transition into the lands.

..............Buckshot

[4060MAY]

the gas cutting starts at the base and goes half way up the bullet.
Been freezing rain here and i haven't been able to go to my friends and take pictures.
He tried smaller patching yesterday 16/2400 and at 20' the bullet went sideways thru the target.
the bullets are lubed with lee sizing wax, anything more and the accuracy went really south at 100yds, from 2-3" groups to 18" groups. altho not sure if it's the leading or the lube. once we find ONE constant , then it's a matter of elimination

Buckshot
there is no transition, the rifling starts at the end of the chamber. no throat and no freebore.
This is a Uberti 38-55 and when we started the rifling looked like it was done with a file, after some break-in and shooting the tops of the lands are smooth, but the bottom of the grooves still look bad.
this gun is no where near as tight as yours, the groove dia as best as can be measured with cerosafe and slugging, is .381-.3815

we haven't tried black powder in it yet.

[4060MAY]

longbow
the patches look like little pieces of black confetti.
never found a piece big enough to evaluate.

[powderburnerr]

black confetti is a good indicator of blow by.The remains should be the same color as when started , , I dont shoot much smokeless but if you are going to shoot the bullet cast hard it works better to wrap to groove diamater with a heavier paper , if you are under bore dia , you should try a softer bullet so it can bump up .. smokeless doesnt bump up a bullet as easily as does black it seems ,..............Dean

[45 2.1]

Sounds like the lead is too hard. What are you useing?

[oso]

Agree with powderburnerr - thicker patch, softer alloy.
Also wonder if Lee sizing lube would work for BP lube since it can mix with water. I use carnauba paste wax or Liquid Alox.

[4060MAY]

This is the trap we built

[4060MAY]

first picture is what i thought was gas cutting. 16/2400
second picture is 30/4895 notice the bullet shortening
still no sign of rifling that is obvious, but it's there
third picture is bullet patched to bore dia, 18gr/2400
at 15ft the bullet went sideways

[4060MAY]

picture show leading with one shot, also the cleaning patches show tears. picture of the patches, and a chamber cast

[4060MAY]

The barrel has a really rough spot about 12" from the muzzle. there is no throat or freebore and the chambering is questionable.

the first thing on the agenda is to lap the barrel and try to get the rough spot out, hand lapped. the next thing will be a throater to just clean the sharp rifling at the chamber transition.

most of the leading was at the throat, probably because it very sharp and the rest of the leading is at the rough spot.

bullet patched to above groove dia. seemed to work better, after we cure the leading problem we will work at 50, 100, 200yds.

There is a match 3-29 so it has to be done by then

[4060MAY]

picture i forgot, tough gettin old.
cleaning after one shot

[oso]

Looks to me like your boolit is lacking sufficient diameter to engage the rifling. Will the unfired boolit pass through the barrel? I prefer my unpatched projectiles to be a thou over bore - just engaging the lands. How do the boolits mike compared to opposing rifling impressions on your chamber cast? Lapping that mold might be a consideration.

[45 2.1]

Your boolit is too hard for the load intensity. Try some 40:1 Pb/Tin alloy.