Gunsmithing School me on reamers please

[earthquake]

I'm new to buying a custom built rifle, and I didn't know one had to specify chamber/throat length. How does one know how long of a throat he needs?

What I'm unsure of is if all ammo/bullet types require similar throat length etc. Where do I start? 0.010" jump? 0.015" jump or more?

I'm shooting a 6.5 Creedmoor and currently only the Hornady factory ammo, but I want to get into reloading asap and try some of the bullets from Berger (130 VLD's), Lapua (136 and 139 Scenar) and maybe Sierra (142 SMK).

I am unsure what to request at this point. Would asking for a 0.010" jump for the 140 and 120 factory loaded Amax bullets be a good starting point?

Thank you in advance, as I'm really in the dark here!

 

[Rthur]

I think this could be something to discuss with your Gunsmith. I would think with your 6.5 creedmoor you have room with this respect. In other words you can seat your bullet out a ways and still fit well in your mags.

R

 

[Edds]

If you are shooting Hornady factory ammo, you should ask for a standard SAAMI chamber.

 

[damoncali]

This stuff has all been figured out so it's not a big deal. Unless you're working with a weird wildcat, just tell the smith what bullets you want to use and to throat it for that. (It goes without saying that you pick a smith who has experience with the type of rifle you're building). I just had a 6mmXC chambered, and asked the smith about what reamers were available - he said he had a .273 neck throated for 115's. It's as simple as that - because that is exactly what I needed. I would have specified a .272 neck if it were up to me (having measured my brass already), but that's close enough, so I went with it.

 

[68bthp]

The 6.5 Creedmoor cartridge is one of the easier ones to choose a chamber for. With the bullet range you mentioned, it just about perfect the way it comes from SAAMI, and there's no alterations necessary to improve performance and accuracy. After weeks of educating myself on the cartridge by reading all the archives and searches that I could find, (and asking questions about my proposed custom dimensions for it that largely went unanswered) I pretty much went with the original chamber...... except I ordered the reamer with a .295 neck instead of a .296. (scarcely a change there) I'm planning on using Hornady brass and 130 to 140 grain bullets, and the loaded Hornady dummy cartrige measures at a .291" neck. So I thought .295 would be snug, and perfect. I kept the freebore at the .199-.200" frebore, as tighter .14- .15 freebore will increase pressure with the longer bullets.

Unlike other cartridges I've done in the past, this is one cartridge that Dave at PT&G really didn't have a lot of guidance about. He is helpful and will mention pros and cons about the different dimensions with it, but he really doesn't want to lead you more one way then the other like he might do more so with the other cartridges. I think that while he is familiar with the 6.5 Creedmoor, he doesn't have years of experience and tons of feedback from shooters like with some of the more established cartridge chambers. So try to study up on it and know how it works. Unless a smith is REALLY experienced with a particular cartridge (and you sense this when talking with him), I wouldn't really entirely trust going in blind and just letting them dicatate what you should go with. You've got t have an understanding of the cartridge dimensions so you can follow and understand what the smith is recomending. (and feel if it sounds right for you or not)

 

[earthquake]

Thanks for the advice. That's a lot to think on. So freebore would be the quantity known as "jump" for the bullet to reach the rifling? This is different based on whether or not your bullet has a tangent or secant ogive, correct?

 

[BillCh]

Thanks for the advice. That's a lot to think on. So freebore would be the quantity known as "jump" for the bullet to reach the rifling? This is different based on whether or not your bullet has a tangent or secant ogive, correct?

Yes, that is correct.

I remember freebore as the length of the free space forward of the case mouth before the bullet begins to engage the rifling.

It stands to reason that the freebore is the biggest factor in considering seating depth and 'jump'; the angle the throat is cut at can't help but affect OAL as well. An example off the top of my head of two ends of the tangent - secant ogive spectrum would be the 77 gr. MK vs. the 75 gr. Berger VLD. It's hard for me to imagine that a throat angle cut specifically for one would be good for the other.

Something else you may want to think about is how much of the bullet shank is in the case. Longer OAL will give you more room in the case for powder. You'll have more fuel for the heavy's but the shorter, lighter, bullets may not enjoy the extra jump. Then there is the magazine issue - if you have one.

Decide if you want to shoot one bullet or compromise, light or heavy, mag length or single load. Its a mighty deep rabbit hole.
You can obsess about this stuff. I do.

Good luck with your research.

B

 

[bricktop]

Another option is to get a chambering reamer with no freebore, then use a throating reamer to cut your freebore to the desired length. You would make a test cartridge with the desired OAL, then incrementally cut the throat until it chambered without jamming - then a small additional depth for whatever jump you want.

 

[swhiteh3]

So much fantastic information here. Thank you!

Based on all this, I'll be ordering a standard SAAMI chamber, which is what my gunsmith recommended as well. (I'll be shooting factory Hornaday 140gr A-Max to start, but might want to move to reloads later on).

Tag for any future discussion. Thanks again.

 

[Deadshot2]

I just went through this same process only for my .308. The barrel maker, who I also had true the action and install the barrel, suggested that I go with a "No Neck Turn Match Reamer. Basically a SAAMI spec reamer only with a shorter freebore so I don't have to run the bullets out beyond magazine length for a reasonable jump. The dimensions are at the lower end of SAAMI spec so the brass doesn't expand as much as in larger chambers leading to far longer brass life when reloading.

The reamer they used was ground by JGS to accommodate the most common factory match ammo's such as Fed GMM.

If you haven't had the barrel chambered yet, consider this route, using a "no turn match reamer".

 

[LRI]

We have two 6.5 Creeds on the shelf. One for each of the popular bullet configs. (Factory and the boogers)

Both are setup to be mag tolerant in the AI stuff.

Be happy to help.

C.

 

[Edds]

We have two 6.5 Creeds on the shelf. One for each of the popular bullet configs. (Factory and the boogers)

Both are setup to be mag tolerant in the AI stuff.

Be happy to help.

C.

What is the freebore on your reamers?