284 seating depth question

[KYpatriot]

Hey y'all Dave Kiff of PTG suggested that I buy a reamer with .188 freebore for the 180VLD and .160 for the 162amax.

I would like to shoot both, but want to focus on getting the 162amaxs to shoot since they are so much cheaper and do everything i want out to 1000.

So, if I throat this rifle for the 162amax at .160, and the want to shoot out to 1500 and switch to the 180vld load, I will have to seat them a little shorter. I dont have my components yet, so how much powder capacity am I giving up with the 180VLD having to seat them to the shorter freebore of the 162amax? I mean .028 sounds like nothing to me, am I missing something?

 

[Dave-O]

Re: 284 seating depth question

Are you wanting to single feed them, or run them from a mag?

Are you wanting to touch the lands or are you planning to jump them

PM turbo54 He says he has a .088 freebore reamer, see how close he is to the lands

 

[KYpatriot]

Re: 284 seating depth question

This will be built on a surgeon long action so I won't have any limitations on COAL other than the case itself. So I if I set the 162AMAX out as far as possible (not sure what COAL that would be, dont have my components yet), and then set the freebore .160 out from that, then it seems to me that the 180 VLD still ought to shoot pretty well. Also as the throat erodes, won't that mean that the freebore will slowly work towards the advantage of the 180? Am I thinking wrong here?

 

[turbo54]

Re: 284 seating depth question

KY: I don't have all the mathematics in front of me, but I calculated the reduction in case capacity for 7mm bullets to be .035gr/.001".

That means seating .001" deeper yields a .035gr reduction in case capacity. This assumes the boat tails are identical, if you want to compare different bullets.

So, if you throat your chamber .028" shallower for the amax than the VLD, you'll have to seat the VLD .028" deeper than you otherwise would have.

.028" x .035gr/.001" = .98gr

These calcs were based on measureing case capacity of water, and measureing case capacity of powder (tamped/filled as best I could) to establish a powder/water density ratio. Oughtta be close.

 

[turbo54]

Re: 284 seating depth question

Also: The 284 has a rather short neck to begin with (less than a full caliber) so I think its a good idea to have the full neck length in contact with the bullet's bearing diameter. Maybe you disagree, but whatever.

Making use of the entire neck, a 162 amax COAL will be right about 3.100", or 2.380" from casehead to ogive.

Hope that helps.

 

[KYpatriot]

Re: 284 seating depth question

Thanks, Turbo, exactly what I was looking for.

I'm starting to realize that when I call Dave Kiff over at PTG to order I need to specify both the COAL and the freebore to get a reamer that maximizes case capacity. Right?
So I need to send a loaded round or something?

I just dont understand all the inconsistency. So many are shooting 180VLDs in long action 284s and I dont think I have heard anyone with the same throat on their rifles yet.

Just so I'm sure, the term "freebore" means the distance from the first point on the ogive of the bullet that is full caliber to the beginning of the lands, correct? So if I am specifying a chamber that number is really only half the equation, I also specify a COAL to go with it. You can have a freebore of .188 at 2.9"COAL or 3.1"COAL right?

-So if you wanted a chamber that maximizes powder capacity with the 162AMAX AND provides optimum freebore for that bullet what should the specs be?
-If I have plans of trying the 180VLD as well, should I spec to that bullets optimum freebore and COAL instead, and let the amax make the jump?
-How sensitive is the amax to seating depth anyway?

This stuff is all so much more complicated than my 308. My Rem5r has about a mile of freebore and the 175SMKs shoot the lights out in that gun. But I know the secant bullets care about freebore and I want to get this chamber just right.

 

[turbo54]

Re: 284 seating depth question

KY:

Freebore/throat (same thing) is the portion of the bore that has had the rifling cut out.

Imagine if the reamer didn't cut ANY rifling lands out... only the ogive of the bullet would be outside the case!

"Optimum" freebore is a touchy, somewhat subjective voodoo. In general though, you want to set it so that:

1: You have the option of seating bullets to touch the lands...and
2: Your cartridge will fit in the magazine...and
3: Your bullet is deep enough in the casemouth to keep it aligned and retained...and
4: You can maximize case capacity...and
5: You have some room to "chase the lands"

What COAL can your magazine accommodate? Lets start there.

 

[lostcoyote]

Re: 284 seating depth question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">Imagine if the reamer didn't cut ANY rifling lands out... only the ogive of the bullet would be outside the case!</div></div>

this seems to be the case with my 7mm A-bolt.

with the lands correctly measured (5x averaged), i seated an Amax162 to be jammed 0.010.

here's the result:

the bullet comparator (sinclair 0.28) stops just at the case neck! there is perhaps 2 hair widths of copper showing... and i can see the land impressions about 0.035 off the neck. arrgh, looks like i need a ream job if i need to get more powder into the case if my max load information is too conservative.

i also tried this with my berger 180 match hybrids.
same thing.

 

[turbo54]

Re: 284 seating depth question

Wow! My short action 284 @ 2.950" COAL hangs the 162amax out further than that!

 

[KYpatriot]

Re: 284 seating depth question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">KY:

Freebore/throat (same thing) is the portion of the bore that has had the rifling cut out.

Imagine if the reamer didn't cut ANY rifling lands out... only the ogive of the bullet would be outside the case!

"Optimum" freebore is a touchy, somewhat subjective voodoo. In general though, you want to set it so that:

1: You have the option of seating bullets to touch the lands...and
2: Your cartridge will fit in the magazine...and
3: Your bullet is deep enough in the casemouth to keep it aligned and retained...and
4: You can maximize case capacity...and
5: You have some room to "chase the lands"

What COAL can your magazine accommodate? Lets start there.</div></div>

Well I was going to use the Surgeon DBM, so I will have to find out what the mag length is. I didnt think it would be an issue at all, figured that there was no way I could be mag limited with the long action 284 but that might not be true.