BRNO 1939 7X57 20.5 inch

[jgh4445]

I have one and am wondering what twist rate this old gun might have. What is the best way to determine?

 

[Alaskan Ironworker]

Use a cleaning rod and a tight fitting patch. The cleaning rod must be able to spin freely, so use one with a spinning handle. Insert said patch and rod into the barrel until the patch engages the rifling, and make a mark on the rod with a marker. Then measure how many inches it takes for your marker mark to make one full rotation. Easy as pie.

 

[Archie]

If you get a 'strange' inch measurement, measure it in millimeters. I would expect BRNO to be designed and manufactured in metric. The spin rate is the same, no matter what, but it may be easier to measure one way or the other.

 

[Dave DeLaurant]

Use a cleaning rod and a tight fitting patch. The cleaning rod must be able to spin freely, so use one with a spinning handle. Insert said patch and rod into the barrel until the patch engages the rifling, and make a mark on the rod with a marker. Then measure how many inches it takes for your marker mark to make one full rotation. Easy as pie.

Ditto.

For the registration mark, I wrap masking tape around the rod and then draw a "T" with a Sharpie at the front sight, the top of the letter flush with the muzzle. The position of the leg of the "T" will indicate when one revolution is complete, and the distance to top of the "T" provides the length.

I do it a couple of times, just in case the patch or jag unthreads a bit -- a tiny bit of gun oil to lube the patch may or may not be helpful.

 

[Dave DeLaurant]

BTW, is your Brno half- or full-stocked? A buddy of mine has one of these in the same chambering with a beautiful full-stock.

 

[Dr T]

Shouldn't that be "Easy as 2 pi"?

 

[gobsauce]

Shouldn't that be "Easy as 2 pi"?

Hahaha, that's a nerd joke. I get it, 2pi is a period of a standard sinusoidal or cosinusoidal wave!

 

[Dr T]

And exp i(2 pi) is a full rotation of exp (ix) where x is the twist...If you get all of the units exactly right it starts getting really sick.

I just couldn't help it...

 

[Jim Watson]

SAAMI standard is 8.75"/222 mm. Search says 220 mm in Europe.
Of course the tight patch test will show you for sure.

I saw a cased Rigby rifle at a gun show with a letter from W.D.M. Bell, famous small bore elephant killer, expressing concern; did the .275 Rigby made for their 140 grain semispitzer have fast enough rifling twist for the regular 175 gr roundnose? Search shows Rigby made rifles for both loads but I did not see anything to say whether the twist was different or if it was just different express sight calibration.

 

[eastbank]

i always liked the 7x57 cartige, from the first 98 mauser i bought as a young man. as a left hander i bought a new rem 700 sps in 7mm08 with a 20" barrel when they first came out and it does every thing the 7mm mause did-does and being left hand a big plus for me. i think the twist is 1-9 or 1-10 and it handles bullet weights from 120 gr to 175 grs.