Advice on chamber for 308

[BuildingConceptsllc]

So, I bought this barrel from a nice guy on here, and its a sweet one too. I was going to start the load work up process and I noticed the chamber seems to have been cut different than my last 308 barrel that BMP did for me.

Distance to lands (175smk)-BTO- 2.20 (it actually seems to be under that, I had to push the bullet much harder than I normally do to get that number).

My previous load had a BTO of 2.260"(with 20 or 30 thou jump I think) and it was pretty good for the 175gr SMK that I like to shoot. So, I guess what I'm asking is this.

If the chamber were at 2.300" that would give me a COAL of right at 2.87 with no jump using that smk175 (which I definitely would jump,) but it should also allow me to be at the lands for a similar sized VLD or something I think...

Is this chamber just set up to run smaller bullets? To get my speed without pressure issues, I'm going to need more Freebore if I want to run 175gr smk again, right? So I just need to send it to a competent Smith to cut my chamber to work with my 175-185gr preffered bullet right?

What about the neck size area of the chamber? What size would I want that to be with lapua brass? Or do I just need go measure a bullet in a case and go what .002"-.003" beyond that, more? ---- I should also add that I want to use a bunch of federal brass I got for loading and stock piling to shoot out of this gun, for ammo that I'm not so worried about picking up my brass or the uh oh ammo pile.---


I've been reading a good bit and found some info in accurate shooter but I'm not certain about a few things so I thought I'd ask here. Did t see any threads here that nail this particular thing down but if I missed it, point me that way and I will read em. Thanks guys.

 

[BuildingConceptsllc]

Couple things.

CBTO is a comparator type of measurement. Your measurements mean nothing to anyone else because the comparators used to derive the measurements aren't made to any standard. It is definitely the measurement you want to use for setting your does up, but just not universal to what other people will see. COAL is more meaningful when speaking about a universal loaded round length.

.308W is like 6BR. There's a shit ton of reamers out there. It's hard to tell what you'll get when buying a barrel second hand. As you're finding out. If you're serious about your own chamber specs you are money ahead just buying a blank and having your guy chamber it. Setting back a second hand barrel is getting expensive.

For neck clearance it seems like some guys think they only need 2-3 thou over a loaded round neck diameter and some guys like 4-5 thou. Me personally, I don't see the point in cheaping out on clearance. I don't wear brass out by overstretching the necks. I'm a 4 thou guy.

At this point you could just buy a throating tool and open the freebore up or have it rechambered. I would just do the former. It's the cheapest fastest way of getting your chamber where you want it. Or you could completely start over and have it rechambered which negates buying the barrel second hand.

Yeah I know CBTO is a relative measurement, that's why I provided what the COAL would be at the given CBTO. Is there some other way I should give the info or better way?

4 thou on the neck size sounds good to me, I don't want it rubbing and I need to check the thickness of a loaded Fed case round with that bullet too.

I think it's only like 80 bucks or so to have the chamber throat lengthened a little but I might have made that up. I don't just want to lenghten the throat but I can't shoot the bullet I need to shoot with this short of a chamber so, I've got to do something.

If I did get a reamer, what's the process to do that myself? Is it done with a hand tool? I've never done that but I'm a very accomplished wood turner and wood worker so, I feel sure I could do it. Thanks for info.

 

[BuildingConceptsllc]

It's pretty easy. You're just turning a reamer by hand instead of using a lathe.https://www.midwayusa.com/product/100717692

The link isn't quite working. Exactly what type of reamer would I need to get? I will see what I can find on YouTube about it too

 

[BuildingConceptsllc]

It's a hand throating reamer. I paid $165 for the three I own. At this point I have them for .22, .243, and .264. It's the same concept as chambering pistol barrels by hand. It allows me to take whatever saami chamber and open it to my desired length.

View attachment 7831833

Yeah there's just a lot of different ones with slightly different names and I didn't want to get the wrong one. Not sure it's worth buying one though for 308? Wish I could rent one from someone who had one and mail it back to them when I'm done with it. If it was 6mm or even .264 that would make more sense but I probably won't ever shoot this barrel out and do another, at least not for a very long time. I bet someone here would let me rent theirs, but if not I can buy one, just need to make sure I get the right one but shouldn't be that hard. I'm very hesitant to ever buy another ptg product after their gauges I got that David Manson still has actually I think.

 

[BuildingConceptsllc]

I have a post in the px. Midway looks like they will have to order it and it will be a few months before they can get it. I like the stop set up on that one, and that's also the one they used in the video I watched so hopefully I can find one like it. Thanks for the help! I appreciate it a lot.

 

[Average guy]

Search 4d reamer rental. They may have a rental throating setup.

 

[CaptNemo]

If you have a bore scope, I'd take a look and the rifling lead before you get carried away. There may be carbon build up in that area keeping you from getting a "True" measurement with the comparator tool.
It might save you from removing steel that doesn't need to be removed.

 

[BuildingConceptsllc]

If you have a bore scope, I'd take a look and the rifling lead before you get carried away. There may be carbon build up in that area keeping you from getting a "True" measurement with the comparator tool.
It might save you from removing steel that doesn't need to be removed.

I have. It's never been shot and is clean as a whistle. The chamber looks very good actually, it's just too short for what I want to do

 

[BuildingConceptsllc]

Search 4d reamer rental. They may have a rental throating setup.

Yeah I found them online but it was kind of unclear to me exactly what it was that they would be renting and it looked like they didn't have a 30 cal available anyway.

 

[smoothy8500]

kind of unclear to me exactly what it was that they would be renting and it looked like they didn't have a 30 cal available anyway.

Looking at Reamer Rentals which I've used in the past, have throating reamers but the 30 cal is probably out right now. You should call them to get in line for the rental. The only issue is that the throating reamers cut really fast and you'll end up with something longer than what a Remington factory barrel would have.

Throating Reamers

Honestly, it's better to find a smith with a little experience than trying to figure it out on your own....

 

[BuildingConceptsllc]

Looking at Reamer Rentals which I've used in the past, have throating reamers but the 30 cal is probably out right now. You should call them to get in line for the rental. The only issue is that the throating reamers cut really fast and you'll end up with something longer than what a Remington factory barrel would have.

Throating Reamers

Honestly, it's better to find a smith with a little experience than trying to figure it out on your own....

Yeah my buddy is a Smith and he has a reamer, I just hate to always be asking him to do stuff for me. He won't let me pay him but I bring lunch for his whole shop over about once a month or so as a thank you, which they all seem to like pretty well( 5 guy), but still I hate to always have something I need him to do. He told me to come by Wednesday and Frank G was nice enough to send me a few drawings as well as give me some advice on it so, I think I'm in good shape now.

 

[smoothy8500]

reamer has an adjustable stop so you can cut in .005" increments if you wish.

Have you actually used one?

Yeah, just giving friendly advice to be careful..... There's no reference point on a throat reamer as to "where" the reamer starts in relation to the existing chamber with the stop. Well, at the time I couldn't figure out how to find it without trial and error.

Micrometer Reamer Stop - 4D Reamer Rentals

Precision, repeat-ability, and ease of use: these are the benefits of P. O. Ackley Micrometer Reamer Stop. Now you can do production runs with your Chamber Reamer, without having to index each workpiece axially. You’ll be assured of consistent headspace, chamber after chamber! To set up, insert...

4drentals.com

 

[BuildingConceptsllc]

Welp..... I ended up getting my buddy to rent me a finish throat reamer from 4D. I watched a YouTube video and went at it. I'm not sure if I want to leave it where it is now (OAL BTT, w/ 175smk) 2.791", I thought about going another .020" to get it to 2.811" OAL with a 175smk but not sure if I should?

 

[Baron23]

Yeah my buddy is a Smith and he has a reamer, I just hate to always be asking him to do stuff for me. He won't let me pay him but I bring lunch for his whole shop over about once a month or so as a thank you, which they all seem to like pretty well( 5 guy), but still I hate to always have something I need him to do. He told me to come by Wednesday and Frank G was nice enough to send me a few drawings as well as give me some advice on it so, I think I'm in good shape now.

In that case upgrade to steaks on the grill and beer/booze. This price will assuage your guilt! Haha.

Best of luck,

 

[BuildingConceptsllc]

In that case upgrade to steaks on the grill and beer/booze. This price will assuage your guilt! Haha.

Best of luck,

Fortunately, he only had a chamber reamer, but he rents stuff from 4 D often and so he found and rented the uni throater for me. It came in yesterday, and I did the deed last night. Not sure if I want to go 20 thou more or not though. Also not sure how even it should look when using a bore scope. Looks pretty even but not preferably even. Though that's what all the other throats I have looked at generally look like. These pics show the biggest difference between lands and groove start/stop point, which isn't all controlled by the throat reamer of course. It can only cut what's there's already but I think it looks pretty good right?

 

[Praeger]

Yeah, just giving friendly advice to be careful..... There's no reference point on a throat reamer as to "where" the reamer starts in relation to the existing chamber with the stop. Well, at the time I couldn't figure out how to find it without trial and error.

Micrometer Reamer Stop - 4D Reamer Rentals

Precision, repeat-ability, and ease of use: these are the benefits of P. O. Ackley Micrometer Reamer Stop. Now you can do production runs with your Chamber Reamer, without having to index each workpiece axially. You’ll be assured of consistent headspace, chamber after chamber! To set up, insert...

4drentals.com

That is a micrometer stop for a chamber reamer, not a throater. Chamber reamer has a thicker shank, throater is smaller.

You'd want this one: https://4drentals.com/products/precnecknthrt/

 

[BuildingConceptsllc]

That is a micrometer stop for a chamber reamer, not a throater. Chamber reamer has a thicker shank, throater is smaller.

You'd want this one: https://4drentals.com/products/precnecknthrt/

Correct. That's exactly what I got and it worked really well. I found the starting spot by running the nuts all the way down then went out by 20 thou at a time, just because I had so much I was removing I wasn't worried. Then I measured, and cut about 10 thou at a time, cleaned with brake cleaner, measured , re oiled, cut again..... until I reached my depth. I will probably end up going 20 though more to match a chamber that Frank Green sent me drawings for that he also wrote the OAL with a 175smk down for me on it. (Which I will share if someone needs it, just pm me). It gave me a lot more confidence to know where I was trying to go with that drawing. I didn't go quite as deep though yet, still trying to decide on that one but I probably will go 20 thou more to get to an OAL of 2.811 using a 175smk bullet. (Base to tip)

 

[BuildingConceptsllc]

Well after looking at the measurements on my last barrel that BMP did for me, I decided to extend the throat a little more. I also did the last of the depth a little differently and it gave me a very even final cut . I used my left hand to stabilize the handle and cut the final three times only cutting .0025 at a time. I also flushed it with oil and used a bunch of oil while doing so. I got very good results doing it this way.

Final measurement are:

OAL base to tip- 175SMK = 2.8350"
BTO- 175SMK= 2.6650"( #8-30 comp)

My other barrel was .030 longer throat but 2.811" OAL with 175smk is a size that some use when chambering so I figured right in the middle of those two lengths would be good for me. I can reach the lands if I need to but also can jump and still have good case capacity so I feel like this will serve me well. Here's pics of the final throat.