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Where to seat rounds for OCW test on new build.

 
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  #1  
Old 08-18-2010, 07:53 PM
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Where to seat rounds for OCW test on new build.

I'm getting ready to break in and work up a new load for my upgraded Howa 308. I have leftover 165gr Interbonds loaded with 44.5g of varget. I'm trying to figure out where to seat the IB's for my OCW test and wanted to know where the lands were on my new Broughton barrel as a starting point...

I measured some old factory ammo I have lying around and also pushed some bullets I have (165 Interbond, 165g Scirocco's, and 168g SMK's) into a FL resized piece of winchester brass loaded into my MCR Howa 308. After ejecting the chamberd test piece I measured with my calipers using a stony point bullet comparator (measured at ogive) and also for OAL just using the calipers. Here's what I got:

Round, Comparator Meas. Inches, OAL inches, Note.
Fed Prem. SGK 165gr, 2.125, 2.686, Factory Round.
Win SuperX 150gr, 2.178, 2.708, Factory Round.
Fed Fusion 165, 2.16, 2.718, Factory Round.
Hornady IB 165, 2.253, no meas, As Loaded into Lands.
Swift Scirocco 165gr, 2.221, 2.866, As Loaded into Lands.
SMK 168gr, 2.267, 2.873, As Loaded into Lands.

the average of the factory round measured at ogive on comparator was 2.154
Average for factory OAL was 2.704 (most of these are sp hunting rounds)
I have a couple rounds loaded up for my old Tikka with OAL of 2.802 which was almost max for the tikka Mag...measured at the ogive these are 2.182

For the IB's in the HOWA I slotted the empty case to seat the bullets by chambering the round and measured OAL and with the comparator. The average on hte comparator was 2.247"
The average for these OAL was 2.870

Average differences between factory and hand chambered to lands was .093" delta measured on the ogive and .166" delta for OAL on average...

Question is to what length do I seat these bullets for the OCW test for which I'm reloading, starting with the Interbonds...? It looks as if the factory loads are 0.1" off the lands...

The Howa is an internal drop floor mag so I should have a bunch more room than the Tikka (max was a hair over 2.8" OAL). Where do I start seating? .04" off the lands .02", or .01" off or .09" off the lands like the factory loads?

Help or discussions greatly appreciated...

Matt
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Last edited by zupatun; 08-19-2010 at 12:30 PM.
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Old 08-18-2010, 08:28 PM
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Re: Where to seat rounds for OCW test on new build.

How far off the lands to start isn't a fixed thing, most of us pick something we've had good luck with and start trying to find a good shooting charge. I've had good luck around 30 thou off the lands with most cartridges so that's about where I start. After finding the best powder charge I'll do seating tests moving both in and out.


Where do I start seating? .04" thou off the lands .02" thou, or .01" off or .09" off the lands like the factory loads?

Not real sure I follow your figures. In your first instance, I doubt you really mean to start 40 micro inches off the lands, which is what .04 thou off the lands amounts to. If you mean 40 thou off then that's okay too.
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Old 08-19-2010, 12:50 AM
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Re: Where to seat rounds for OCW test on new build.

Matt,

I'm wondering how you come up with the middle/center load for your first OCW test?

What I do is shoot a 10 shot ladder test and find what I think is a node. Then do the OCW around the higher velocity node, if there is one.

Any suggestions on eliminating those first 10 shots?
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Old 08-19-2010, 08:12 AM
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Re: Where to seat rounds for OCW test on new build.

Roy,

Can't say that I have enough confidence in my reloading or my shooting to nock out ten rounds from the test...but with the 308 I'm not worried about burning out my barrel. I start where Dan Newberry recommends which is 7% below max recommended charge for my bullet and caliber. That's where I'm starting with the .308 and the 165IB--41.2 gr working up in 2% increments to 46.9 (stopping earlier if I see pressure signs etc) or maybe one increment more. The middle of this is about 44gr which is close to where I settled on my Tikka Varmint in 308.

I have asked Kirby (Fiftydriver) if he thinks his method the "no load development load development" -- starting just below max recommended load, working up to sticky bolt lift and then backing it off 2 grains--would work for the .308 (if I got that correct).

I reload, but just don't have enough data, experience or talent to make a recommendation, just sharing my thoughts and plans.

Apologies.

Matt
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Old 08-19-2010, 08:37 AM
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Re: Where to seat rounds for OCW test on new build.

"I have asked Kirby (Fiftydriver) if he thinks his method the "no load development load development" -- starting just below max recommended load, working up to sticky bolt lift and then backing it off 2 grains--would work for the .308"

You asked, what did he say?

I've never been comfortable with any "backing off" number in grains. Backing off 2 gr. in a .22 Hornet is a lage reduction by percentage andmnot much in a .340 Wea., but it should be good in a .308.
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Old 08-19-2010, 09:01 AM
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Re: Where to seat rounds for OCW test on new build.

Quote:
Originally Posted by boomtube View Post
You asked, what did he say?
I'd say that Kirby would say something like, "Where the max load is is between 90 and 150 grains, the 2 grain below max seems to work well."

In my 270 AM the top load that is backed off 2 grains is when after 2 shots the primer pocket is shot. With the finally settled on load case life is maybe 4-6 shots.

I don't think one would want to do that w/a rifle such as a 308. It just doesn't make sense.

You may want to try using an equivalent of 2 grains in percentages.

Here's what happens when you do what I do. (I'm sorry to say I did it but the economy needed the boost) It's even more full now!

Last edited by royinidaho; 08-19-2010 at 09:38 AM.
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Old 08-19-2010, 12:16 PM
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Re: Where to seat rounds for OCW test on new build.

Quote:
Originally Posted by royinidaho View Post
I'd say that Kirby would say something like, "Where the max load is is between 90 and 150 grains, the 2 grain below max seems to work well."

I don't think one would want to do that w/a rifle such as a 308. It just doesn't make sense.

You may want to try using an equivalent of 2 grains in percentages.
That's exactly what I asked for advice...whether it is 2 grains or it is a percentage and for his specific recommendation for the 308 case and bullet combo.

The specific (initial) example he gave was 93gr Retumbo for a 300 RUM...and 2 grains is a hair over 2% (2.15%)...

Also, No I haven't heard back yet, but he's a kinda busy guy so I didn't expect an immediate answer...

We're all pretty much on the same page.

Matt
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