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Max Online: 16728 @ 03/25/12 08:51 AM
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#6315698 - 05/29/16 09:06 PM POI after mods.
TKM Offline
Woodsman

Registered: 01/29/12
Posts: 156
Loc: Bedford, Tx.
To start, I like the Thompson Pro Hunter platform. Mostly due to looks, overall length, easy to handle. Have had a 243 for a few years, then a custom 338 barrel, bought a 270 and 30-06 barrel last year to tinker with. In the past I reloaded everything, my die set covers about two dozen calibers. Now days I don't have much time for that so was looking for factory loads. Had a difficult time finding something that would group better than 2" in the 270 and 06 so I decided to shorten the barrels. With the scope rings removed I could only cut about 3 1/2" in my lathe so that's what I did to all but the 338 (integrated muzzle brake on it). Put a similar crown as from factory but had to deal with the flutes so I rounded them off. Came out looking nice. Yesterday I went to a friends gun range up in Oklahoma to see if this helped. Results were great, shooting factory loads I could easily get less than 1 moa, with the 243 had a group of three touching. What I found interesting is this. After reinstalling the one piece scope mounts and changing scopes around, all three barrels shot right at 6" low and 5" to the right. I expected them to all be different. Didn't take but a few shots to get them back to 200 yard zero. Not worried about anything, just found it interesting that all three after having this much work/changes done were all in the same area after. Really happy with the accuracy improvement after removing 3 1/2" from the barrels and this is my first time cutting and re-crowning.

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#6315702 - 05/29/16 09:09 PM Re: POI after mods. [Re: TKM]
FiremanJG Online   content
THF Celebrity

Registered: 12/16/08
Posts: 24491
Loc: Wolfe City, TX
Zeroing at 200 yards, you lost muzzle velocity cutting the barrels shorter, therefore you have more bullet drop, is my suspicion. The drift to the right, was there a left to right wind?
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#6315715 - 05/29/16 09:17 PM Re: POI after mods. [Re: TKM]
TKM Offline
Woodsman

Registered: 01/29/12
Posts: 156
Loc: Bedford, Tx.
No wind. I know I lost some velocity, just found it interesting they all were the same 6 down and 5 right. Keeping the scope mounts with the barrels but swapping scopes I expected them to be different from each other. That being said, I was shooting some 80 gr GMX's in the 243 before cutting, used 55gr bt's after. Expected them to be a little higher.

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#6315745 - 05/29/16 09:33 PM Re: POI after mods. [Re: TKM]
FiremanJG Online   content
THF Celebrity

Registered: 12/16/08
Posts: 24491
Loc: Wolfe City, TX
I see a very long list of cartridges that, from a hundred yard zero, drop very similar at 200 and 300 yards.
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#6324860 - 06/06/16 11:12 AM Re: POI after mods. [Re: TKM]
Nitro27 Offline
Tracker

Registered: 11/06/12
Posts: 598
Loc: Terrell,TX
I think it is more the barrel whip and harmonics of the Thompson Center rifles that you fixed more than the loss in velocity. There is something to them having a shorter barrels. Mike BEllm has a few hypothesis on why this happens and has has good results.
if you are into Thompsons check him out.

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#6324877 - 06/06/16 11:36 AM Re: POI after mods. [Re: TKM]
TKM Offline
Woodsman

Registered: 01/29/12
Posts: 156
Loc: Bedford, Tx.
Yes, I agree with the harmonics, which is why I cut them down. Velocity loss isn't why they were 6 low.

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