Freebore and OACL Question and Help

[Chappy6mm]

New to posting but not to this site.
I have been reloading for several years now and most of it was for factory Rem 700s in 223, 22-250,270, 7mm mag, and 300 win mag. Can get good accuracy out of stock guns by bedding, trigger tweeking and precise reloading (several groups under .5 MOA).

My question concerns a gun I just bought from a gunsmith at a show. It is a 6mm-.284. It is a Rem 700 action with a Shilen barrel in 1-12" twist. Smith said to shoot the 68 gr - 80 gr berger bullets that the gun loved them. So after ordering a set of 6mm-284 dies and finding some 6.5-284 Lapua brass I was ready to go last night. Being new to forming wildcats this went very well by just running the 6.5 284 brass thru the 6mm 284 FL resizing die.
When trying to find the lands of the rifling is where I ran into something new. The bullets I have will not reach the lands to set my OACL. I usually start out at .020 and fine tune from there.

Bullets I loaded include Berger 68 gr / Nosler 70 gr / and Watson 75 gr Match

I went forward with the loads by just setting the bullet far enough into the neck that I felt good about controlling runout.

This morning I realized I had a box of 95 gr Noslers and thought I would see if I could find the lands with them. Well I did. The OACL for the 95ers was 3.035 and that was touching into the lands. The 95s will probably not stabilize in the 1-12" twist so I am wanting to make the others as accurate as possible

To the Question

The 95 gr Noslers touched the lands with a OACL of 3.035
The 70 gr Noslers have an OACL of 2.940
Assuming the ogive is the same on these two noslers I am JUMPING bullets .095

IS it OK to jump them that far?
How much can I jump bullets accurately?
Bullets are only seated .09 into the neck Is that enough?
The farther I seat them the more they will jump.

Thanks in advance Looking forward to discussions on this site!!!!!!!

 

[Deleted member 46119]

The jump is fine from an internal ballistics standpoint.

From an accuracy standpoint, well, you'll just have to see.

I'd spend a little time with JBM - Bullet Length List and JBM - Calculations - Stability

or

Berger's same.

 

[Chappy6mm]

Thank You

Why do you think the smith used so much free bore in a 1-12" twist if it was meant to shoot the lighter bullets?

 

[MagnumManiac]

Generally, there will be 2 OAL that produce the best accuracy, one real close to the rifling and another much further away, .200"+ is not unheard of.
I have a few rifles with throats longer than what I would call ideal, but I get very good accuracy out of them even with the longer throats. What I do is load to the max magazine length with 5 rounds, shoot a group and see if it shoots, if it's not up to par, I load 5 round batches with decreasing OAL's by .005" increments, not going too short within reason, I stop at .050" less if nothing changes and go back to .010" short of max mag length. This has only happened to me with one bullet type, all others have had some improvement within the .050" limit I set.
In fact, I have one rifle with a very long throat, due to it being a Weatherby chambering, and it is very, very accurate, one hole groups @ 200yrds are common................... and it's a 375Weatherby! Not noted as being a tack driving cartridge but mine is, it's a Winchester Model 70 Classic Stainless circa early/mid '90's rechambered and hand lapped in a HS Precision stock, 300yrd shots are easy with this rifle, I'm still flabbergasted by it's accuracy.

So, I wouldn't worry too much by how much the bullet jumps, just tweak your seating depthnuntil you come up with an accurate OAL, after all it's the barrel whip that you're tuning, not the jump.

Cheers.
gun)

 

[Chappy6mm]

Well after shooting today I think I have a keeper.

My largest 3 shot group was .69 and the best was .33. That was with a 16 power scope so I feel I can do better.I guess it doesn't hurt to JUMP them

It is going to be okay for bullets 80 gr and under.
Not exactly what I want for 600-1000 yds but a good100-400 screamer.

After complaining about the gun to my step father about having to stick with the lighter bullets he sold me his unfired 6.5 WSM. It is also on a Rem 700 action with a Douglas Premium 1-8 twist barrel. Going to shoot 140 grainers out of this one. Cant believe he had this gun in the back of the safe and didn't tell me about it till now
Now I have the best of both worlds