OAL .338LM CIP with A-Tips

P

peterdobson

CGN Ultra frequent flyer
Business Member
Rating - 100%
109   0   0
Location
Halifax
We will be loading 300 grain A-Tips in our CIP- chambered Timberwolf. A recent suggestion is an OAL of 3.750" which is about .13" off of rifling. Any experience offered would be appreciated.

Regards,

Peter
 
To me, the only factors that matter when choosing a COAL or CBTO are, in descending order of priority:

- does it fit in the magazine?
- distance from ogive to lands (aka jump) versus what you want this distance to be
- is the base of the bullet where I want it to be within the case
 
Thanks adamg, single feed only will be used.

I think that we will try zero and various "jumps" to determine best accuracy.

Regards,
Peter
 
peterdobson said:
Thanks adamg, single feed only will be used.

I think that we will try zero and various "jumps" to determine best accuracy.

Regards,
Peter
Click to expand...

For anyone unfamiliar with the techniques to determine where "zero jump" length is, Erik Cortina has a pretty good video on his technique. Basically you just seat the bullet really long, put case lube on the bullet, then chamber it in your rifle and close the bolt (take safety precautions so you don't set one off!). Then aggressively open the bolt, and gently pull bolt back and remove cartridge. Measure its length now (either CBTO or COAL) - this should be your "zero jump" aka "jam" length.
 
peterdobson said:
Thanks adamg, single feed only will be used.

I think that we will try zero and various "jumps" to determine best accuracy.

Regards,
Peter
Click to expand...

Zero jump or just touching the lands is the worst possible seating length. The reason is that there will be a natural, if small, variation in seating depth which will result in some rounds being 1 thou into the lands, some rounds being just on the lands and some being 1 thou off the lands. Either go fully into the lands or stay at least 0.010" off the lands.

For single loading, OAL is irrelevant.

Don't measure seating depth to the bullet tip. You need a measurement to the ogive. Bullets vary considerably in OAL and the seater doesn't operate off the tip. Trying to measure off the tip of the bullet will give you an ulcer as the numbers will vary constantly.
 
Thanks - we are familiar with Cortinas method. Agree on zero jump for correct reason stated. We are actually into lands about .003" - barely discernable rifling marks. Will try incremental lengths off of lands in .005" increments, as OAL(ogive to lands) is a crucial aspect of accuracy. We have not had any feedback with anyone using these except for mag-feed at 3.750", but we are sure that there are others.

Will try with N570 this weekend.

Regards,

Peter
 
Last edited:
When running 300 A-Tips in the EnABELR I load them 20 thou off the lands, and am well pleased with the accuracy.

It was the first seating depth I tried, and it worked so I didn't play any further.
 
I know you were only asking about CBTO, but something else I noticed about A-Tips: They do dent on seating much more easily than a Scenar ot Berger OTM.

If you aren't using their specific seater stem I found mandrelling/neck sizing the brass to a 1 thou hold (fine for single feeding) helped a lot.
 
Thanks Harwood:

We'll watch chambering. We put the Hornady A-Tip seater into a Whidden seater die - perfect fit. The A-Tips have zero "wobble" with this seater compared to the Whidden seater stem. We note that various shooters are using the Forster seater.

Regards,

Peter
 
OP,
Since you are single loading-

Load to a hard jam at your discretion.
(1/2 land/groove length as width)

This will ensure that the brass is properly head-spaced to the bolt breech face instead of assuming the extractor is working in your favor.

Once you ladder loads, you will know visually what your max powder quantity is by primer appearance.

Seating the projectile deeper will NOT affect pressures noticably...w/o instrumentation.

Anneal &/or turn necks for low ES/SD.
 
You must log in or register to reply here.
Back
Top Bottom