Primer Size Question

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Primer Size Question

Postby dogsniper » Fri Jul 27, 2012 6:26 am

This may seem like a silly question...but I am hoping T can weigh in on this.

All the load data I am finding for the 450B calls for small rifle primers. And to the best of my knowledge, Small rifle Primers are actually smaller in diameter than Large rifle primers. My question is this....

Since we know that the 450B is Hornady/Bushmaster's version of Tim's 45Professional, and he developed that round from the 284Win brass....and 284Win Brass uses a Large Rifle Primer (according to load data)....When/how did we get from Large Rifle Primer pocket size to Small rifle size?? And why? And an even bigger question is...IF a person does try to use 284Win brass in place of factory 450B brass for loads, with the large rifle primer, what changes in charge weights if any should be used to start working loads up??

I hope I am not the only one that has ever wondered this...and maybe I am way overthinking it...but curious minds just gotta know...

Thanks all
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Re: Primer Size Question

Postby Hoot » Fri Jul 27, 2012 7:32 am

I don't know the decision history as I was not around at the time. Hornady and Bushmaster tweaked Tim's design just enough to make it inconvenient to make your own ammunition from spent .284 brass. Bless their hearts. :roll:

In practice, there is a slightly thicker wall in the .284 which reduces the case capacity a little. That results in higher pressure all else being equal when translating Hornady brass loads to Winchester. Drop back a grain and retest. If you use a hot small rifle primer like the Rem 7 1/2 (personal favorite), WSR, or GM205M, I doubt you'll see much performance change with a large rifle primer, given the fast powders (by rifle standards) we are using.

Use the "search this forum" feature about 2 years back for a thorough discussion on the difference between the two brass.

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Re: Primer Size Question

Postby wildcatter » Fri Jul 27, 2012 8:15 am

Hoot wrote:I don't know the decision history as I was not around at the time. Hornady and Bushmaster tweaked Tim's design just enough to make it inconvenient to make your own ammunition from spent .284 brass. Bless their hearts. :roll:

In practice, there is a slightly thicker wall in the .284 which reduces the case capacity a little. That results in higher pressure all else being equal when translating Hornady brass loads to Winchester. Drop back a grain and retest. If you use a hot small rifle primer like the Rem 7 1/2 (personal favorite), WSR, or GM205M, I doubt you'll see much performance change with a large rifle primer, given the fast powders (by rifle standards) we are using.

Use the "search this forum" feature about 2 years back for a thorough discussion on the difference between the two brass.

Hoot


Dogsniper,

Hoot has it right here. Hand loading has a skill set, that requires the loader to always start at the lower pressures levels and work up, even if you are given a proven safe load. That's our job and safety is Our responsibility.

As you have noted, and where Hoot has expanded on, there will be some minor differences when using the Win 284 case and you must be ready for them, expect them, and react to those differences, in a safety conscious manor.

As too the decision to use a small rifle primer size.

There were two things that stuck out, Heads-Over-Heels.

First, the Match Guys have pretty well proven, for the most part, that small rifle primers, are the Primers to use, in most rifle cartridges, if accuracy is an important goal. Noticed, I said .."pretty well proven", this thesis, doesn't hold true for every Cartridge, bullet, load, and yes Primer, combination. However, one merely needs to shoot, our chosen poison, and the wisdom of that decision, comes immediately to the fore-front, and in Spades, I might add. I've told this story before, and this looks like a good place to repeat it..

.."In the early days, there was a camera crew from the Outdoors Channel and a Talking-Head, that recorded a Zero Inch, 100yd group, with the 450 Bushmaster/Hornady ammunition. All on Camera, as in verified and indeed they took the paper in and got the Zero Inch Group verified, using real Target Measuring Tools (I guessed it to be a three shot group, but from two individuals, one of which was actually there, as a witness, the other, who had only seen the program, both telling me it was a Five-Shot-Group). This being hard to believe, even for the Program Team, none the less, they finally declared the 450 Bushmaster, The-Most-Accurate-Rifle, in the world, and fellow reader, they did this, all on Camera"!!..

Second, the small rifle primer decision, was as a favor to us. The Small Rifle Primer Pocket, "Greatly" increases, the strength of the Web area, Allot. Need I say more, about Safety Margins??

..t
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Re: Primer Size Question

Postby dogsniper » Fri Jul 27, 2012 10:25 am

Thanks to both of your for your input and detailed information. It makes perfect sense about making the webbing stronger (I probably should have figured that out myself), the point about small rifle primers being the choice for competition...I must admit I did not know...as I have never done that type of shooting, and all my reloading is simply for hunting rounds...start low and work up as stated. I have found the importance in this many years ago when I worked up a load for my Browning A-bolt that was "hot", but the rifle shot it great ....1/2MOA. I was younger and foolish, and tried that same load in a different rifle.....VERY difficult to open the bolt. That lesson I will NOT forget

Thanks again for all the help guys!
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Re: Primer Size Question

Postby pitted bore » Tue Jul 31, 2012 9:27 am

There is another aspect of primer size selection in the 450B that becomes significant when using heavier charges of slower burning powders.

In a cartridge loaded without powder, the primer almost always has enough energy to drive the bullet well up into the barrel and wedge it into the lands. A LR primer will usually have more energy than a SR primer, so that the bullet from a case with a LR primer pops out of the case quicker and wedges further in the lands than the same case with a SR primer. When the primer drives the bullet out of the case, the result is to increase the size of the combustion chamber for the powder. This lowers the efficiency of powder burning. Thus a LR primer can result in less efficient powder burning. I suspect this effect is more pronounced in straight cases like the 450B than in cases with a neck.

So, there's a trade-off in using LR vs SR primers. A LR primer starts the powder burning faster than a SR primer, which raises pressure and may make the powder burn more quickly than a SR primer. The LR primer also enlarges the combustion chamber quicker, which lowers pressure and may make the powder burn less quickly than a SR primer. Which effect predominates will depend on a whole lot of factors, like case capacity, case shape, powder type, powder amount, primer "strength", bullet type, throat conformation, etc. ( almost ad infinitum).

In using lighter bullets in the 450B, my very brief trials with 284 cases with LR primers did not show any improvement in velocity or efficiency of powder burn with LR primers. I suspect I was at the point where the better ignition with the LR primers was balanced by their production of greater chamber expansion. With heavier bullets it may be that the weight of the bullet could counter the greater primer force of the LR primers sufficiently to increase pressures with a resulting higher velocity.

I don't know whether Hornady had any of the above in mind when they specified the SR primer.

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Re: Primer Size Question

Postby Hoot » Tue Jul 31, 2012 10:51 am

I'll tell you. After around 1500 loads, I had my first squib in the 450b a month or so ago and that small rifle primer drove the 160gr Barnes TAC XP bullet into the lands tight enough that it took a couple of strong smacks on my reloading rod tipped with a dummy plug to knock it out. I could not tell that the primer had even gone off. Through my plugs I heard and felt the hammer drop click, but that was all. At first I thought I did not have the action all the way in battery as I was hand cycling single rounds at the time. That of a bad strike/primer. After waiting 30 seconds, when I jacked back the charging handle, I immediately knew what happened. :roll: What a mess. Powder in all sorts of places I didn't want it to be. Took me 20 minutes to strip everything on the cleaning table at the range and shake, brush, swap, blow with a soda straw, all of it out, including the magazine. Image

Bob's right though. With light bullets and not creating sufficient neck tension, the likelihood of delayed powder ignition or flat out squib load goes up with large rifle primers. If someone ever comes up with a solution that creates a reproducable, consistent, non-scarring, easy-to-implement, strong crimp for this caliber, we all should toss 'em a buck. ;)

Hoot

PS: A month later and I'm still getting flecks of that unburned powder charge out of my rig.
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Re: Primer Size Question

Postby pitted bore » Tue Jul 31, 2012 12:30 pm

Hoot-
Slightly off tropic, but related to your last post:

In a couple of my adventures with the 450B and other cartridges in which the primer went off but the powder did not, I''ve noticed that the powder lost its graphite coating and appeared as yellowish grains, which I understand is the native color of nitrocellulose. I''ve read reports in other forums making the same observations. Did this happen with your incident? Just curious.

(And for the uninitated, note that the click with no bang is a significantly undesirable result of pulling the trigger. When powder does not ignite immediately, it may still ignite later and produce some very high pressures. Tim/wildcatter has been warning about this in the forum since the forum began three-plus years ago.)
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Re: Primer Size Question

Postby Hoot » Tue Jul 31, 2012 5:35 pm

pitted bore wrote:Hoot-
Slightly off tropic, but related to your last post:

In a couple of my adventures with the 450B and other cartridges in which the primer went off but the powder did not, I''ve noticed that the powder lost its graphite coating and appeared as yellowish grains, which I understand is the native color of nitrocellulose. I''ve read reports in other forums making the same observations. Did this happen with your incident? Just curious.

(And for the uninitated, note that the click with no bang is a significantly undesirable result of pulling the trigger. When powder does not ignite immediately, it may still ignite later and produce some very high pressures. Tim/wildcatter has been warning about this in the forum since the forum began three-plus years ago.)
--Bob


I was half expecting to see that, but no. The majority of the powder (Alliant 2400) which is usually easy to set off, was in one mass, but about one third was loose. In retrospect, if that ever happens again, after waiting a while, I'll separate the upper from the lower and then jack it open slowly with the muzzle pointed down. That should afford some control over where the loose powder winds up. Obviously the best solution is to not have it happen again.

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Re: Primer Size Question

Postby LlindeX » Thu Aug 02, 2012 3:41 pm

Hoot,

Do you have any idea what might have or probably did cause the failure to ignite that you had?

Just wanting to learn as much as possible from your incident.
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Re: Primer Size Question

Postby wildcatter » Thu Aug 02, 2012 7:40 pm

LlindeX wrote:Hoot,

Do you have any idea what might have or probably did cause the failure to ignite that you had?

Just wanting to learn as much as possible from your incident.


Myself, I've seen this most often with under-charged cases, which the delayed ignition is sometimes the cause of on-set Detonation or a Pressure Wave Event..

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