New 700LTR 308. Why such a long throat? How far to set the bullet? Pressure?

[SeattleDude]

I am sorry if it was covered before, I am new here.

I have new 700LTR in 308

Trying to figure out seating for my rounds.

Length of the chamber measured with Hornady OAL gauge to where the bullet touching lands and it is 2.332 measured with Hornady Comparator (base to ogive)

If I load 168gr Hornady HPBT at 2.810 OAL then it measures 2.201 with bullet comparator. That is .134 JUMP to the lands!

If I load 168gr A-max at 2.810 it measures 2.175 and that is .157 JUMP!

What should I do? How long should I seat them? How would I adjust the powder charge? (I understand that pressure actually increases with longer bullet seating in rifle)

Little help needed.

ps. Powders I have on hand - Varget, CFE223, IMR4064, AA2230 and RL-15

 

[BoilerUP]

Most popular 168/175 30 caliber bullets are very jump tolerant in 700s with stupidly long freebore.

Load to the max length your magazine will allow, find the best charge weight via normal load development, then shorten OAL if necessary to find optimal accuracy.

 

[Mad_Charlie]

Most popular 168/175 30 caliber bullets are very jump tolerant in 700s with stupidly long freebore.

Load to the max length your magazine will allow, find the best charge weight via normal load development, then shorten OAL if necessary to find optimal accuracy.

This is good advice.

If you want to single load, you can seat way long (which will give you more case capacity, which usually lowers pressure, which usually means you can/need to increase powder charge) and you still may not find the lands, depending on bullet, and still have any bullet in the case.

But it will most likely shoot pretty good anyway...

 

[roggom]

Shoot the Amax or sierra MK, the ogive is jump friendly. The Hornady HPBT can be finicky until you get the jump right.

For me, my rounds must fit in the internal mag, so most times I am seating around 2.828-2.831. Pressure is good, submoa groups from an sps tac and varmint, not stellar but I am content.

Yeah, sux both of my rifles swallowed a no-go guage like a used up hooker. Free bore and loose headspace, but I made it work.

BTW looks like Grafs is dumping their blems, these are SMK blems, just not shiny like a new SMK but for the price they shoot damn near the same

https://www.grafs.com/retail/catalog/product/productId/26342

 

[SeattleDude]

Thank you for heads up about Grafs sale. I just ordered 400pc of 168 seconds and 200pc of 175 seconds and a short handle for my Forster Co-Ax ! Free shipping and no handling fee.

 

[MitchAlsup]

Your numbers are within 0.003 of where those bullets touch the lands in my M700.
This is what happens when lawyers run rampant.....

 

[TommyAtkins]

The chamber is throated from the factory for the heaviest bullet that could possibly be fired in that caliber, probably 220grs. You can get decent accuracy (I get 3/8") but the only way around it is a new barrel with a tight chamber. As already stated , the lawyers get involved and things get designed for the lowest denominator.

 

[judgedelta]

Mine shoots pretty good ( the minus factor is me) loaded to 2.8; but it's a lefty...

 

[User22]

Hey, I have a question I'm sure one of you have the answer to... What is different from using a OAL gauge vs. finding the COAL vs. the old fashion method of placing a bullet in a mock, empty case. covered with permanent marker, and pushing it up slowly with the bolt in the chamber??? By using the last method. you get to find out the max. length where the bullet is seated, to touch the lands, "I think"... I've always done the latter and just used my calibers to adjust seating from there. So please, if you have a more precise way of doing this or if I'm all jacked up, feel free to help.... Thanks

 

[MitchAlsup]

I use the old fashioned method with one change--the case chosen is known to fit with less than 0.001 of clearance on the bolt.
Otherwise the ejection plunger can push the case forward enough in the chamber to create inaccuracy.

 

[Recreational Shooter WA]

Hey Seattle Dude,

I have a .308 that also has a very long throat, very similar to yours, and I've found with the SMK's that I still get very good accuracy seating the bullet to magazine length, which is around 2.840" or so, which gives it something like .080" of jump (approximate numbers).

Using 190gr. Berger VLD's, I MUST seat them around .040" off the lands to get acceptable accuracy. Any other jump results in terrible accuracy, but at the .040" it shoots quite well.

The difference is due to the design of the bullet's nose or ogive. Bullets like the SMK have a tangent ogive, while the Berger VLD's, Hornady AMAX and VMAX (and others) use a secant ogive. Bullets with a tangent ogive tend to "self center" themselves better than the secant ogive bullets, which allows them to be more tolerant of long jump lengths. Secant ogives tend to have higher ballistic coefficients though.

Here is a good article to read more about these concepts.

Tangent, Secant, Hybrid Ogive Bullets within AccurateShooter.com

 

[SeattleDude]

Thats a good read! I ordered few hundred of 168 and 175 SMKs

Hey Seattle Dude,

I have a .308 that also has a very long throat, very similar to yours, and I've found with the SMK's that I still get very good accuracy seating the bullet to magazine length, which is around 2.840" or so, which gives it something like .080" of jump (approximate numbers).

Using 190gr. Berger VLD's, I MUST seat them around .040" off the lands to get acceptable accuracy. Any other jump results in terrible accuracy, but at the .040" it shoots quite well.

The difference is due to the design of the bullet's nose or ogive. Bullets like the SMK have a tangent ogive, while the Berger VLD's, Hornady AMAX and VMAX (and others) use a secant ogive. Bullets with a tangent ogive tend to "self center" themselves better than the secant ogive bullets, which allows them to be more tolerant of long jump lengths. Secant ogives tend to have higher ballistic coefficients though.

Here is a good article to read more about these concepts.

Tangent, Secant, Hybrid Ogive Bullets within AccurateShooter.com