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Forum Index > Precision long range hunting and shooting > 8 twist 7mm with the berger 180 pr 175 and tumbling

8 twist 7mm with the berger 180 pr 175 and tumbling

26 Apr 2019
@ 09:42 am (GMT)

Rod

New member here.

I have been reading and watching your video about your experience with the eld and berger bullets. Now concerned and need some help.

I am avid hunter for many years alot if it with bows although I have also befor that hunted with various rifles and pistols.

This year on the elk hunt going to take a rifle in 7mm mag as I have had one for many years and like it. So I bought a tikka tx 3 and was going to re-barrel in and have on order in for 8 twist barrel using the berger twist rate calculator To either shoot the 180 berger or 175 eld amd maybe try the 195 berger for potential long range shots.

All that I have talked to have said the faster 8 would be fine and not affect the accuracy including a phone call with Berger.

Watching you video on the practical you state in the text that using a fast twist can cause 10 in error! I just watched your annealing video and you say you have a gun there that is doing bullet tumble.

So I have a 8 twist barrel on the way also just bought a browning xbolt hells canyon long range with 26in barrel in 8 twist now in the way but it wont be here until June and onlybhave deposit down.

I was getting ready to the break in on the tikka usongn168 gr bullets but now am so concerned about theb8 twist thing on the 180 berger I am thinking about cancelling the barrel order and the xbolt order and just shoot the 168 bergers or the 162 eld. I want to be good to 800 yds.

Advice???!!

Replies

26 Apr 2019
@ 10:33 pm (GMT)

Paul Leverman

Re: 8 twist 7mm with the berger 180 pr 175 and tumbling
Rod, somewhere in the forums (I'm not very good with "search") there is a very elaborate dissertation about twist rates for the 7mm. I don't recall exactly what was said, but I'm pretty sure the 1:8 was not the ideal rate.
27 Apr 2019
@ 10:23 am (GMT)

Iain

Re: 8 twist 7mm with the berger 180 pr 175 and tumbling
Hi Rod.
My understanding is that tumbling with 8" twist is not the problem.
The problem seems to be bullets coming apart under the stress of the high revs generated by the combination of a big horsepower 7mm (Practical, STW, RUM etc) and the 8"twist.
From what I have read here and elsewhere, the coming apart seems to be confined to the 180 ELDM, which would make sense, as it has a thinner jacket than some others. I don't know about the 162 ELDM under the same conditions, but then most who opt for an 8" twist do so planning to use the very heavy and long projectiles.
Whether not the 7RM with an 8" twist can generate enough velocity and consequently revs, to cause a problem, I have no idea.
You mention the 175 ELD - that would be the 175 ELDX, which has a heavier jacket than the ELDM. My only experience with the 175ELDX is that it would not stabilize in a 9.5" Sako 7 RM. Maybe it would in 9". The 162ELDX is fine in the same rifle BTW. ELDXs are pretty long.
 

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