Tickled with my new (old) GPR - anything I should check for before shooting?

[Rileybassman]

I can't tell you anything except I got it in the early eighties as I stated. The rifle was in the gun store five years prior and no one would buy it so I did. It must have been made in the late seventies? It was a very fine rifle.
How did you determine what twist you have?

There are threads here that I found that helped... I used a jag with a tight patch, rammed it all the way down, took some masking tape, and carefully put it around the ramrod right at the muzzle and put a mark that lined up with a reference point (used the front blade). I then carefully/gently pulled the rod out and let it twist itself until it rotated 90 degrees and then measured how much rod had come out - end of bore up to masking tape - and then multiplied by 4 to get the full rotation. I got exactly 12" to a quarter ram rod rotation... so 12"x4"=48". I was expecting it to not be super exact and take several tries... but it was bang on exactly 12" first try. Longer twists would be 15 or 16" to a quarter rotation so it would be apparent IMO pretty quickly if you have a longer twist.

 

[LME]

There are threads here that I found that helped... I used a jag with a tight patch, rammed it all the way down, took some masking tape, and carefully put it around the ramrod right at the muzzle and put a mark that lined up with a reference point (used the front blade). I then carefully/gently pulled the rod out and let it twist itself until it rotated 90 degrees and then measured how much rod had come out - end of bore up to masking tape - and then multiplied by 4 to get the full rotation. I got exactly 12" to a quarter ram rod rotation... so 12"x4"=48". I was expecting it to not be super exact and take several tries... but it was bang on exactly 12" first try. Longer twists would be 15 or 16" to a quarter rotation so it would be apparent IMO pretty quickly if you have a longer twist.

Looks like you got it right? I am wondering if they made a 48 and a 66 inch twist? If they did it is the first time I heard of it.

 

[Rileybassman]

Looks like you got it right? I am wondering if they made a 48 and a 66 inch twist? If they did it is the first time I heard of it.

Check post 20 here... I have heard a couple others confirm it as well for .54s:

https://www.muzzleloadingforum.com/threads/great-plains-rifle-rate-of-twist.89518/

 

[Henry Miles]

Make sure you don't over tighten the lock screw going thru the stock. Snug it down but don't tighten it much more if any. The stock won't crack if you don't tighten the screw. The 1:48 twist will shoot PRB's well with lower charges of 3F (70-90gr). I have the same rifle and love it for the weight/balance and performance. Nice find.

 

[UndeadPoet]

Love it!! she's a beauty as well! Shoot good for ya?

I am ashamed to say that I have not yet had the pleasure…but I “aim” to remedy that real soon.

 

[LME]

Check post 20 here... I have heard a couple others confirm it as well for .54s:

https://www.muzzleloadingforum.com/threads/great-plains-rifle-rate-of-twist.89518/

I don't get what post#20 has to do with what we are talking about. It just said he had a drop in barrel ? He didn't say he did or did not have a Lyman? Did I miss something?

 

[UndeadPoet]

I picked up the exact rifle last Fall. Mid 1985 vintage according to Lyman and also a measured 1/48" twist. One doe already fell to a 54 PRB in January' BP season with it.
Though I have scoured the bore with Scotchbrite, lapping compound and elbow grease, it still shows shredded patches, sometimes, using 80 grains of FFFg. These GPR's are known for their sharp lands. Next outing I'll try FFg to see if there is any difference.

You might also try a patch over the powder before you load your PRB. That is supposed to make a huge difference in patch shredding.

 

[Rileybassman]

I don't get what post#20 has to do with what we are talking about. It just said he had a drop in barrel ? He didn't say he did or did not have a Lyman? Did I miss something?

 

[Billy Boy]

Most .54s from the 80s are 1:48”.

My 54 GPR, 2003-2004’ is 1:60

 

[Rileybassman]

Make sure you don't over tighten the lock screw going thru the stock. Snug it down but don't tighten it much more if any. The stock won't crack if you don't tighten the screw. The 1:48 twist will shoot PRB's well with lower charges of 3F (70-90gr). I have the same rifle and love it for the weight/balance and performance. Nice find.

Good to know... I went and checked and I had it "snug" but not tight... I backed it off a 1/4 twist to be safe... just past where it freely spins.

 

[Rileybassman]

My 54 GPR, 2003-2004’ is 1:60

Yea my understanding from Lyman is post 1990 the non hunter .54 GPRs are the 1:60

 

[Billy Boy]

Yea my understanding from Lyman is post 1990 the non hunter .54 GPRs are the 1:60

I think that is right. The GPHunters were all 1:48,:across all years. I don’t know if they made any fast twist sabot guns 1:22 or 1:28, almost seems like they did. I’ve been very confused for months at a time so I could have seen it in a vision..

 

[LME]

View attachment 125975

I just got off the phone with Lyman. I was told they had a few early rifles that had a 1 in 48 twist. These rifles were even older than mine and there are very few of them. Some kind of a mistake? You are fortunate to have one.. I doubt you will ever see another. There were other Lyman rifles with several different twist

 

[Rileybassman]

I just got off the phone with Lyman. I was told they had a few early rifles that had a 1 in 48 twist. These rifles were even older than mine and there are very few of them. Some kind of a mistake? You are fortunate to have one.. I doubt you will ever see another.

That's very interesting... yea the post made it sound like there was a mistake. There's a couple guys on here that have them... learning the history on these has been very fun!

 

[LME]

That's very interesting... yea the post made it sound like there was a mistake. There's a couple guys on here that have them... learning the history on these has been very fun!

When in doubt go to the one who knows for the answer! LOL!

 

[longcruise]

They made a ton of 1:48 rifles between intro and 1990. After that they were 1:60. I don't think there's any with 1:66 unless they are aftermarket barrels.


The Great Plains Hunter I think was 1:32. Any other info on that

 

[Rileybassman]

For kicks and giggles I just went and re-measured twice and took pics to show my work lol... I'm no scientist, but it definitely seems to be 1:48... and pulling the ramrod out to 15" is definitely a third of a rotation, not a quarter.

Also put a pic of the stamps and first 4 of serial for anyone interested/smarter than me who can tell things I can't

 

[longcruise]

You prompted me to dig out my original gpr barrel. First four are 1441

 

[SmokepoleSam]

longcruise you are correct the GPH is 1in32.

 

[LME]

They made a ton of 1:48 rifles between intro and 1990. After that they were 1:60. I don't think there's any with 1:66 unless they are aftermarket barrels.


The Great Plains Hunter I think was 1:32. Any other info on that

I mentioned 1 in 66. I meant 1 in 60 ! all my other M.L.s are 1 in 66. My error.