Weird OAL problem

[lurcher]

I just had my 7mm saum rebarreled. It is a remington model 7 so it has a short magazine. With the factory chamber I could not get anywhere near the lands with bullets seated to magazine length.

A friend of mine with the same rifle had the exact same problem. He got PTG to build him a reamer that was designed with a short throat so that bullets (162 amax) could be seated to the lands and feed out of the mag. He got a new barrel and had it chambered with this reamer. His rifle performs well despite the loss of powder capacity (he shoots around 63-64 grains of VV N165 and uses a 4inch drop tube to pack it in).

Anyhow I borrowed his reamer (it is a floating pilot reamer with throat built in) and sent it off to my gunsmith with a new barrel. I just got the rifle back and I got to work taking some measurements to start building a load. I measured the chamber OAL (base of bullet to lands) using a hornady tool, and also did the slit neck/seat a bullet, and the cleaning rod with brass tip and two sliding collets techniques. All gave surprising long OAL's way longer than magazine length, The throat is even slightly longer than the throat in my factory tube. I didn't have any amaxes on hand I used 160 accubonds, and these are blunter than 162 amaxes

I then made some dummy rounds seating bullets at lengths that fit with my measurements (10 thou shorter) and they chambered without resistance or changing length.

What has happened here? has my gunsmith run a throating reamer into the chamber (he apparently didn't have a 7mm saum reamer). Or perhaps he has used another reamer? He has a good reputation as a gunsmith and I thought I had stated my intentions clearly.

The only other issue I noticed was that head space was a little tight. It was set with a PTG saum go gauge I purchased. I had to bump the shoulders of new rem brass back a thou to get it to fit the chamber, but I figured this was not a bad thing as brass stretch would be minimal.

I will ring the gunsmith on Monday to talk this over, just wanted to get a feel for what might have happened.

 

[lurcher]

Well i measured both rifles side-by-side that were chambered with the same reamer that was supposed to allow the 162 amax to reach the lands yet still feed out of the mag and they both had long throats. dummy loads seated to touch the lands were 160thou longer than the magazine.

My friend had just loaded up close to mag length rounds and went shooting. he had never measured his chamber. A quick look at the etching on the reamer and it says 180 free bore 1 degree thirty so I guess there was a communication issue with the reamer design........

 

[Jim See]

Thats the same free-bore on my reamer I use on the guys f-class rifles. Probably a good .100-.130" too long for a SA repeater

 

[therifler]

I can offer this advice if you chamber for the short throat you will no longer have a 7 saum . it will now be what ever you choose to call it . the 150 tho. freebore is what makes it efficent in its present state. shortening the freebore will loose capacity and require a reduction in powder . moreover even factory loads will probably be unsafe to shoot through the shorten chamber . T.R.

 

[lurcher]

I can offer this advice if you chamber for the short throat you will no longer have a 7 saum . it will now be what ever you choose to call it . the 150 tho. freebore is what makes it efficent in its present state. shortening the freebore will loose capacity and require a reduction in powder . moreover even factory loads will probably be unsafe to shoot through the shorten chamber . T.R.

I have this concern myself (see my other post on asking about reamer specs). I can see that what you are saying will be true for say 180 grain bullets. Would it still be true for lighter bullets (say 140 or even 160 grain bullets?) Powders I am likely to use are ADI2209 (similar to H4350) for 140's and VVN165 for 160. As far as the lost capacity goes my friend who had a barrel set up with the same reamer I mention above has been seating bullets to magazine length. Using a 4 inch drop tube he can get 64 grains of N165 in behind a 162 amax. If he had the short throat I'm sure he would have to back it off considerably. Any idea how much?

 

[JaxCatm]

Hate to put this out there in a painful way but you have two options that I can see. Option (A) get a good single round follower and have at it will longer than magazine length rounds. Or Option (B) if you have a blind box magazine is to have a gunsmith modify the stock and magazine to a longer length. Seems like the single round load idea would be cheaper in the long run. I have a similar problem with one of my rifles and I went the single round route. Haven't hit a situation where I could not drop the second round in and sent it with all that much trouble.