Gunsmithing Can toomuch freebore lead to unsafe jump distance?

[Falar]

I'm thinking about throating a .30-06 REALLY long, as in long enough to load the 208gr A-max to a COAL of about 3.6" and be .020" or so off the lands since I'll be feeding from .300 WM AICS mags and they allow 3.65". My only concern is that if I do this I could never use factory ammo that is loaded to 3.25 or 3.3 or load any bullets that can't be seated out past 3.4 or so. .250-.300 jump just seems like a LOOONG way and I don't know if it is a good idea or not. Don't know if there is a point where too much freebore can actually become unsafe.

I imagine this comes up with guys who throat rifles for 90gr bullets in .223 also. Since they load up to 2.6 COAL with those and factory ammo is all going to be 2.26ish.

 

[AWGunS]

Re: Can toomuch freebore lead to unsafe jump distance?

Weatherby uses large amounts of freebore to allow their cartridges to do what they do.

You would be correct that short fctory ammo would probably produce horrible accuracy, but I don't think it would be unsafe.

Fouling might be an issue with short rounds as well.

Good luck.

 

[Falar]

Re: Can toomuch freebore lead to unsafe jump distance?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BeachGun</div><div class="ubbcode-body">Weatherby uses large amounts of freebore to allow their cartridges to do what they do.

You would be correct that short fctory ammo would probably produce horrible accuracy, but I don't think it would be unsafe.

Fouling might be an issue with short rounds as well.

Good luck. </div></div>

I think throat erosion would also be an issue besides extra fouling and poor accuracy.

I'm probably going to do this anyway as I have 1000s of 208s to use up. It would be a shame though to lose the versatility of the '06 though, but in reality I would never use factory ammo anyway.

 

[Advokaten]

Re: Can toomuch freebore lead to unsafe jump distance?

Lots of older european rounds have in US eyes huge freebores,

7x64, 8x57, 7x57R, 6,5x55 and a few others,

no the results are not always poor accuracy or erosion on the contrary however the free bore has to have the right design,

and I belive that had a lot to with the angles of the start of the lands.

So the answer to the question is no, there should be no pressure issues, however I must ask why would you have the throat cut that long?

to sort of prove a concept?

/Chris

 

[bohem]

Re: Can toomuch freebore lead to unsafe jump distance?

I wouldn't advocate it. My 30-06 was cut from a standard PTG 30-06 Springfield reamer. I seat the 208's at 3.405" and the base of the boat tail is about 50 thou below the shoulder/neck junction. It is a 10 thou jump to the lands.

If you ran them at 3.6" COL you could fit an extra grain or 1.5gr of powder in there at the cost of throat/barrel life and more than likely, accuracy.

I just solve the problem by shooting a 103-105% compressed load.

 

[Falar]

Re: Can toomuch freebore lead to unsafe jump distance?

The point of the long throat is the 208gr A-max is a very long bullet. Since I have magazine space available I would like to seat the bullet as far out as possible to increase usable case capacity. When I was using 208s in .308 I was loading to 3" and some load them even longer.

 

[palma]

Re: Can toomuch freebore lead to unsafe jump distance?

I asked about throat damage and was told don't worry about it:

http://www.snipershide.com/forum/ubbthre...rue#Post1380071

I personally believe standard throats are for the birds. Go long and don't shoot factory.

 

[bohem]

Re: Can toomuch freebore lead to unsafe jump distance?

Falar, if you ran the throat out so that the base of the bearing surface is at the base of the neck, then you might push the COL to 3.45 or 3.475", but at 3.6" long how much bullet would still be in the neck at that point?

I do enjoy the mag space on the 700 LA's for the 30-06 based cases, but the difference in how much powder I can fit in a 208 in my rifle with a compressed charge safely and how much will actually fill the case to the brim is about 3.5grains

You're still going to have to stick some amount of the bullet in there, even at 1/2 caliber being held in the neck you'd be looking about 1.75-2 grains of capacity increase by quick estimation. The 208 is very long, I'm just wondering if the hassle involved is worth it.

Then again, I'm thinking about RL22 for a powder, you might actually get an appreciable gain (75 fps or more) with RL17 or one of the N5xx powders.

 

[Falar]

Re: Can toomuch freebore lead to unsafe jump distance?

I haven't actually mocked it up yet but the 208 is SOOO long I was assuming it could reach 3.6 with full bearing contact still. When I get the barrelled action back I will check to see how long I will actually need to push the throat to get the 208s bearing surface out of the body of the case and shoulder.

 

[Falar]

Re: Can toomuch freebore lead to unsafe jump distance?

I plan on using RL-17 and my barrel length will be 28". I'm basically looking to maximize velocity with the 208 and the '06 case.

 

[bohem]

Re: Can toomuch freebore lead to unsafe jump distance?

I'll take a look this evening for you, but I seem to remember doing a similar check myself and being well under 3.6" It was in the high 4's, but that was an off the cuff check that I never wrote down, it wouldn't be the first time that I remembered something wrong.

I'll let you know tonight or tomorrow.

 

[buffybuster]

Re: Can toomuch freebore lead to unsafe jump distance?

If you kept the throat pretty tight, say about 0.001" over bullet diameter, it should probably still shoot pretty well. Actually, Sierra Bullets did some testing on looong throats. You might want to give them a call to discuss their findings and throat specifications.

As for how much is too much jump, I have a FN in .308Win and with my bullets seated to 2.820" (mag length) it jumps .250". Not ideal or conducive to the best accuracy but it still shoots 3/4moa consistently.

 

[swd]

Re: Can toomuch freebore lead to unsafe jump distance?

Your throating reamer needs to be as close to bullet dia. as possible. .0003" to .0005" total over, not per side. A thou would be a little loose.