Slight puzzle

[shootrj2003]

I took the GPR to the range for the second time today,I did better this time my final group at 50yds was five shots four touching in a line about 1 1/2" long l to rt and 1 flyer about an inch high and to the left,dang good group ,but the patches were blown to bits ,I took pictures but I'll put them in tomorrow ,I originally used .018 patches last week they were way to tight,so I measured the bore,.519 the lands .503 and the ball .494,I came up with . 013 patches so I had some and took them today,still too tight ,I went to .010 better but still tight I had some uncut cloth in my bag this is .008and used it and the groups
got nice and tight and I could even start the ball with my thumb ,so I used the stuff with some bore lube sweet group but patches are still shredded,this is a fresh Lyman bought used but I'm positive this thing was never shot by the PO,I cleaned the preservative out of the barrel ,beautiful looking bore .I'm not complaining but the patch thing bugs,any suggestions on thinner ,tougher material?i

 

[BrownBear]

Shoot it more, or if you don't like shooting, try lapping it. :wink:

New Lyman's are notorious (at least to me) for sharp crowns at the muzzle and sharp edges to the rifling. They'll cut patches when starting balls and when shooting that won't cut 100 or 200 shots down the road.

I'd just keep shooting it, but plan for having to go to a little thicker patch once you put those 100-200 shots down the bore.

 

[shootrj2003]

That's what I am thinking too -or Kevlar patches! No man,I love to shoot ,I have trouble finding the time to shoot,I've got more on my plate since retiring than I ever did before.I take care of two granddaughters 6 yrs,and8 mo.and a78 land cruiser project and 77 Sportster out in the barn,I haven't stopped hopping yet but yes I am a shooter that' how I got the name. :shocked2: :redface: :shake:
And I got horns to do too.

 

[GreyWhiskers]

That's a purty thin patch but if you're getting good groups keep using them. I agree with Brown Bear. Continued shooting will only help. Have fun. GW

 

[ohio ramrod]

Cut patches on a new bore are common. As stated you can "shoot it in " or if you want to speed things up with out risk try a bronze bore brush and some tootpaste to give it a light lapping, also some fine emory cloth on your thumb can be used to smooth off the crown. New barrels (in my opinion ) do not require lapping coumpounds to remove burrs and sharp edges left from machining.Lapping coumpounds are for salvaging rough bore not for new bores. Again this is my personal opinion and worth just what you paid for it! :idunno:

 

[Trench]

Sounds like you found your patch combination. I started with pretty thick patches in my latest rifle and I've been going down in patch thickness. I started with a .020 patch and I'm playing with .014 patches now. I might go even thinner like you did just to see what happens.

 

[Maven]

Sam Fadala recommends putting a dry patch or piece of hornets' nest over the powder charge [before seating the patched RB] as a cure for blown/torn patches.

 

[droptine55]

by the post he state .494 rb. maybe going to a .490 rb and a thicker patch. to get the same thickness of rb and patch combination he is getting his groups with. may not not work as well but its a thought.

 

[Maven]

The .490" RB + a thicker patch would be my 1st choice as well. However, the OP doesn't say whether he as a large supply of .494" [cast or swaged] RB's on hand. (I assumed he did.)

 

[shootrj2003]

Yeah I pour my own so I got lots of them ,I may see if I can find some .490's locally and maybe a new mold if they work out,but I can 't whine about these groups and might try the wasp nest too there's lots of them around this old farm,or just shred patches til it's smooth, thanks guys lots of help . :hatsoff: :v

 

[Rifleman1776]

used .018 patches last week they were way to tight

I rarely respond to posts about GPR but will make an exception.
What do you define as "way too tight"? Lead is maleable and a large ball can be seated and shot.
Usually, the larger ball and correct thickness patch (determined by much shooting and testing) will give best accuracy.
Going to a smaller ball for ease of loading, as in a hunting situation, is OK and will degrade accuracy only a little.
My suggestion is to stick with the larger ball and .018" patching, use a proper lube and keep shooting. I'll betcha the patch destruction will go away and groups will improve.

 

[MSW]

i'm inclined to agree with OhioRamrod ... try gently working some fine emery cloth around the crown of the muzzle, and see if that does what you need.

i would not do the toothpaste thing just yet ... see if it's the crown that's cutting the patches first.

also, if you get an arch punch and make some wads (either out of wool or leather) and soak them in whatever bore lube you use, you may be able to put a stop to the patch destruction and still get the nice tight groups.

good luck with your project, and make good smoke!

 

[Zonie]

I think several things are causing the cut patches.

As others have mentioned, the muzzle crown on factory guns almost always has sharp edges.
These will cut a tight patch/ball combinition during loading.

If the barrel has square cut rifling as you GPR does there are always sharp corners on them.
It's too costly for the factory to dull up the edges so they ship it that way.

A good scrubbing of the bore with steel wool wrapped around a cleaning jag will go a long way towards dulling up those edges.
The other way is to shoot about 200 shots thru the gun.

If the patches are showing signs of being burned thru that is to be expected with your patch/ball combination.

Your latest .008 patch/.494 ball combination is .510 in diameter unloaded.
With a rifling groove size of .519 you have a nine thousandths wide leak.

In order to seal the rifling, the unloaded patch/ball size must be larger than the rifling diameter so that all of the patch material that is contacting the bore and rifling grooves is compressed.

With a .490 diameter ball and a .018 thick patch the effective patch/ball size is .526.
In your .519 diameter rifling grooves that would produce a crush of .0035 in the grooves.

IMO, a patch crush of at least .002 is needed to produce a joint that will stand a chance of sealing the bore enough to not burn thru.

With your .494 diameter ball, the .018 thick patch would have a .0055 crush.
Either of these would minimize hot gas burn thru.

If you are happy with the guns accuracy with your .494 diameter ball and the .008 thick patch then keep on using it. Don't be surprised when the patches come out tattered and burned though.

 

[George T.]

I agree with some others here and that is that you need to use a slightly smaller ball (I use .490) and thicker ticking ( I use .018) and the patches. It is hard to compress the ball so the patch needs to be thick enough to seal the bore or you'll get the blow by your getting. In my 58 I had to use ,018 to get the patches to hold up but it requires me useing a mallet to get the ball started! Geo. T.

 

[hoochiepapa]

I wouldn't change a thing-except to add a felt wad over the powder. I had the same problem with my Lancaster, shot good, but the patches were scorched and torn. I added a felt wad over the powder, and the groups shrank and no more burnt patches.
Why change everything?

 

[majg1234]

Agree with Mike on this one,all my rifles and SB get the wool patch over powder and patches thin enough to thumb start no short starter used except on occasion the 40cal.They will all turn in great groups out to 100yrds with this loading method

 

[M. De Land]

Good advise, my GM .45 cut patches for a 100 rounds after I did lap it before threading and installing the breech plug. I only lapped with 400 grit and a poured lead slug, 250 round trips and thought that would do it but not so. That rifled bore by the way in that GM barrel was one of the most uniform for level I have ever lapped.MD

 

[Dean2]

Okay, it shoots great, is easy to load but the patches don't look pretty after being used and that is a problem?. :grin:

Burned through patches usually result in poor groups, particularly at 100 yards, if yours don't, enjoy. Keep shooting it, I would experiment with other ball size, patch and load combos looking for the best accuracy, but if this one turns out to be the best groups I would not worry about the patches being burned.

 

[shootrj2003]

The .008 patch was an improvement in accuracy and patch longevity ,the .018 patch was punching through going in and was not even serving as a patch 1/2 the time and barely so the rest of the time.if you have a .519 bore and a .494 ball the proper size would be .0125 or .013 if that is the next size that you actually have on hand,. eg. .519 - .494 = .025 divide that by 2 and you get .0125 I'm pretty sure my math is right up to this point ,so unless I 'm missing something isn't .018 .005 too big ? Of course .008 is .005 too small also but accuracy wise it works,I think after conferring with everyone here,that I could probably go to a .490 ball and back to a thicker patch and just keep shooting til she smoothes out on her own.
Please enlighten me if I'm not Figuring things right or if I've been overlooking something but this is how I've alway's figured patch size before .I did ask for help and I think we figured that out - so shooting the new barrel is my best choice,not a bad choice!

 

[Zonie]

Use whatever works.

Your calculation for determining a correct patch thickness is based on the idea that a piece of material just touching the rifling groove with no interference from compression is enough to keep a burning gas at well over 5000 pounds per square inch pressure from blowing thru the joint.

My experience in designing jet engines and gas turbines tells me otherwise. Especially if the sealing material is made of a soft fiber.

If I am correct, the flammable patch material in the leaking areas will be vaporized almost instantly.