32-20 BP - importance of bullet diameter

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martinibelgian
Posts: 1609
Joined: Thu Oct 26, 2006 1:20 pm

32-20 BP - importance of bullet diameter

Post by martinibelgian »

Just recently ( yesterday evening) I learned - again - that rifles can be finicky individuals, and that things which appear to be self-evident often aren't.

In this case, I'm still finetuning my Latest BPTR - A BSA 12/15 converted to CF, chambered in 32-30 (30-20 rather, as .308 barrel with 1:12 twist). This in order to use heavier bullets, in this case I was shooting a 151gr 30:1 RN of my own design.

Some time ago, I was shooting some promising targets with bullets sized to .308. Now, the chamber in this rifle has a freebore section .100 long of .309 diameter, so I was wondering if getting the bullet a bit bigger (.3085) would improve accuracy. Sounds logical, no? After all, better bullet alignment...

So I polished out my .308 sizer to .3085, and proceeded to test. Whatever I tried, accuracy just wasn't as good as with the .308 bullets - except that at 1st, I was looking for other reasons: Alloy, lube, cleaning routine,...

Until recently, after checking older targets, I just had to come to the conclusion that the larger bullet dia. probably was the cause for the accuracy problem.

So I ordered another .308 sizer (Lee push-through), and gave it a new test yesterday: Problem found! I was again shooting nice, ragged holes when I did my thing.

I also discovered another issue: I was wiping between shots with 2 WD40-soaked patches (yes, I know! But it works) - the 1st is run straight through, and the 2nd was used to thoroughly clean the barrel, 'pumping' it while pushing it through. After all, when shooting BP, a barrel can never be too clean...

Now, I was shooting 2 nice, clammish groups - 1 centered, the other one at 4 o'clock. both very nice groups, but still 2 groups.

I then tried also pushing the 2nd patch simply through, making no attempt to thoroughly clean the bore, and those fliers were gone... Apparently, barrel condition is is a major factor as to the POI. And I was able to get a pretty consistent POI deviation just by cleaning routine.

I do have to say that shooting this little 32-20 with BP does learn one attention to detail: Everything must be right. If not, accuracy will suffer. However, if everything is right, accuracy will be quite good indeed.
Big BP .45's are less finicky than this, but then I never was able to get this kind of accuracy from those big cartridges.
Also, this is the kind of challenge I like - this little rifle is now getting quite competitive indeed, but one needs to thoroughly understand its management in order to get the best from it.

The next challenge will be getting PP to shoot - again, trying to find the details that need to be right for it to perform. Not simple...
bruce m
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Location: australia

Re: 32-20 BP - importance of bullet diameter

Post by bruce m »

it is hard to imagine that there are some who are incapable of seeing the pleasure and satisfaction of this type of challenge.
onya gert.
bruce.
ventum est amicus meus
GrumpyBear
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Joined: Tue May 15, 2018 6:42 pm
Location: Western,Pa

Re: 32-20 BP - importance of bullet diameter

Post by GrumpyBear »

Interesting reading, and makes one wonder what small detail, like the method of wiping,might improve group size.
gunlaker
Posts: 2764
Joined: Tue Jun 23, 2009 6:16 pm

Re: 32-20 BP - importance of bullet diameter

Post by gunlaker »

My .32-40's are similar in that they are much more sensitive to bore condition than my .45's.

Chris.
martinibelgian
Posts: 1609
Joined: Thu Oct 26, 2006 1:20 pm

Re: 32-20 BP - importance of bullet diameter

Post by martinibelgian »

Yes, things like this do convince me that top accuracy is in the details. And sometimes, logic doesn't really play a role... The hard thing is to try and find a cause between different factors - especiqlly if there are several factos present at the same time.
I started out with cartridge OAL, then determined an optimum powder charge. And now I'm working with optimizing fouling management, bullet diameter and type, primer selection...
Still, pretty confident I'm getting there. When you start shooting ragged holes - even if at 82 yds - prone, with sling and aperture sight, something must be right.
Perentie
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Joined: Mon Jul 21, 2014 9:22 am
Location: Queensland, Australia.

Re: 32-20 BP - importance of bullet diameter

Post by Perentie »

How are you cleaning your Martini,s?
By pushing the patch right through, do you have a hole at the breech and remove the BB or do you do all your cleaning from the muzzle?
martinibelgian
Posts: 1609
Joined: Thu Oct 26, 2006 1:20 pm

Re: 32-20 BP - importance of bullet diameter

Post by martinibelgian »

No, I'm using a flexible delrin rod, and I clean from the breech, the rod can make the 'bend'. No issues there, it's only a bit harder than when the chamber is completely free. So no breechblock takedown or cleaning from the muzzle needed.
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