New rifle eject issues

Talk about the AR15 style rifles chambered in 450 Bushmaster.

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Re: New rifle eject issues

Postby Rklenke » Mon Jan 01, 2018 12:28 pm

Thanks for the info. I will look into some different powders. If the obturation you're talking about is causing increased pressure, I should be seeing some pressure signs as well. My primers look fine, but I'll have to go measure some case heads.
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Re: New rifle eject issues

Postby plant_one » Mon Jan 01, 2018 3:21 pm

Rklenke wrote: Using 300 grain XTP over 32.2 LilGun.


can you clarify if you're using the hornady .452 300gr xtp mag ( #45235) or the hornady .452 300gr HP XTP (#45230)
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Re: New rifle eject issues

Postby Rklenke » Mon Jan 01, 2018 4:12 pm

I have used both to the same result. I get no difference in velocity or point of impact between XTP and XTP mag. I was able to shoot some Hornady factory today and everything cycled fine three shots in a row. I threw in another 300 XTP and it cycled fine as well. I'm at a bit of a loss. I'm going to have to just continue to shoot it and see if I can find any trends.
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Re: New rifle eject issues

Postby Hoot » Mon Jan 01, 2018 4:58 pm

Rklenke wrote:I have used both to the same result. I get no difference in velocity or point of impact between XTP and XTP mag. I was able to shoot some Hornady factory today and everything cycled fine three shots in a row. I threw in another 300 XTP and it cycled fine as well. I'm at a bit of a loss. I'm going to have to just continue to shoot it and see if I can find any trends.


IMHO, Either one of those bullets will do just fine with such a weak powder charge. Assuming the factory load runs close to the 38k pressure mark, 32.2gr of Lil Gun behind either 300gr bullet only runs 22k pressure. That's nowhere near the sweet pressure spot like the factory load runs. That circumstance alone can yield some unpredictable behavior. I'm not talking about POI or accuracy. Heaven knows, there are multiple accuracy nodes as you move up in pressure = velocity. There are subsonic loads that are plenty slow and still plenty accurate. Its about how the case expands in the chamber; how it seals or lets crud leak back into the chamber; how much pressure of that 22k vs 38k is left what the bullet passes the gas sample port, to contribute to the action cycling gas; and the list could go on. Under-loading comes with a degree of added lack of reliability. Kick an XTP Mag out of a 20" barrel at 21-2200fps and they'll cycle reliably. At least that's been my experience using either W296, 300MP and yes, AA1680. The latter fills the case up to 90% when you hit the sweet spot, as an added bonus. The downside is you're throwing almost 10% of AA1680 out of the barrel unburned, assuming you're using a hot primer like the Rem 7 1/2 or WSR. Experimenting with all thus stuff (when its warmer than -15F) is the fun part of reloading.
Continuous Process Improvement is what reloading is for. Not finding what worked for somebody else and mimicking it to cut the cost of shooting. The latter is an added bonus, once you find the recipes your rifle likes through experimentation. No finer feeling on the firing line than discovering that you finally cracked the code. ;)

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Re: New rifle eject issues

Postby Rklenke » Mon Jan 01, 2018 6:01 pm

Interesting that you say 32.2 is a light load for a 300 grain as it is the max per Hornady. I haven't gone over the published loads, but if the pressure is as low as you say, it may be worth a slow work up. I'm already getting 2000 fps with 32.2.

The empty space in the case has made me nervous since day one reloading this caliber after reading quite a bit on "detonation". A full case fill would be reassuring.
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Re: New rifle eject issues

Postby Hoot » Mon Jan 01, 2018 7:19 pm

Rklenke wrote:Interesting that you say 32.2 is a light load for a 300 grain as it is the max per Hornady. I haven't gone over the published loads, but if the pressure is as low as you say, it may be worth a slow work up. I'm already getting 2000 fps with 32.2.

The empty space in the case has made me nervous since day one reloading this caliber after reading quite a bit on "detonation". A full case fill would be reassuring.


I have personally, never loaded a 300 grainer with Lil Gun. Lighter bullets all the time but not 300gr.

The 22k psi QuickLoad pressure prediction is base upon loading those bullets seated to yield a COL of 2.26 inches. If you seated them deeper, the pressure and velocity are predicted to go up, but not to 2k fps, even at a COL of 2 inches. The interesting part is that QL as a rule of thumb, over-predicts pressure and velocity usually be about 10% as a safety margin for misguided reloaders who immediately start at the max load.

I am surprised that you clocked them so fast. I forget, were you using a stab crimp or just the taper crimp. Not that it matters because if you're getting 2k fps, you're not getting that with only 22kpsi. Can't happen with a 300 grainer in this caliber. As a matter of fact, I went off the reservation and tweaked the QL equates to get a 300gr bullet up to 2k fps in this caliber. Not hard with slower powders and longer barrels, but with Lil Gun quickly pushing the bullet at that speed, regardless of how you got it to do that, you will be up into high pressure. Don't rely solely upon primer condition like with a bolt action, to get a feeling for high pressure signs. The best indicator is case head growth. If you get a .001 or more growth from one shot, you're hitting it pretty hard. A lot depends upon your chamber. I once had a 450 barrel with an incredibly tight chamber, like a BR barrel. It too kicked my established recipes out faster than expected, though with little case head growth. It had some extraction reliability issues. It took me a week of evenings to lap it into working properly. Conversely, I've also had a loosey goosey chamber that experienced a lot of case head growth, no matter what load I used. So, while generally a good indicator, not even CHG is an absolute indicator of pressure, but despite what you might expect, high pressure can make cases fail to extract just as easily as low pressure.
So in conclusion, I'm my own Grandpa! :lol:

...and for everyone interested in the ejection problem, I apologize straying off topic, but those of you who know me, know I can't help myself. ;)

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Re: New rifle eject issues

Postby Rklenke » Mon Jan 01, 2018 7:51 pm

I'm interested in how you lapped the chamber, I will probably be doing some googling. My barrel/chamber is an 18" budget GLFA. It has given me 80-100 fps over published velocities both in reloading and with Hornady black. Here is a string of 300 grainers for reference. I've got quite a few more like this with averages from 1970 to 2000.

Description: 450BM 300 XTP mag 32.2 LG
Distance to Chrono (FT): 10.00
Ballistic Coefficient: 0.200
Bullet Weight (gr): 300.000
Shots
# FPS FT-LBS PF
6 1964 2569.92 589.20
5 1961 2562.08 588.30
4 1946 2523.03 583.80
3 1962 2564.69 588.60
2 1962 2564.69 588.60
1 1959 2556.85 587.70
Average: 1959.00
StdDev: 6.57
Min: 1946
Max: 1964
Spread: 18
True MV: 1970.14
Group Size (IN): 0.90

I use the Hornady taper crimp, seating to the cannelure (2.080 on the 300 XTP) and crimping to .476. The shorter COAL allows for perfect function from an unmodified pmag 10, which is nice.
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Re: New rifle eject issues

Postby Texas Sheepdawg » Mon Jan 01, 2018 9:47 pm

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Re: New rifle eject issues

Postby Hoot » Mon Jan 01, 2018 9:51 pm

Rklenke wrote:I'm interested in how you lapped the chamber, I will probably be doing some googling. My barrel/chamber is an 18" budget GLFA. It has given me 80-100 fps over published velocities both in reloading and with Hornady black. Here is a string of 300 grainers for reference. I've got quite a few more like this with averages from 1970 to 2000.

Description: 450BM 300 XTP mag 32.2 LG
Distance to Chrono (FT): 10.00
Ballistic Coefficient: 0.200
Bullet Weight (gr): 300.000
Shots
# FPS FT-LBS PF
6 1964 2569.92 589.20
5 1961 2562.08 588.30
4 1946 2523.03 583.80
3 1962 2564.69 588.60
2 1962 2564.69 588.60
1 1959 2556.85 587.70
Average: 1959.00
StdDev: 6.57
Min: 1946
Max: 1964
Spread: 18
True MV: 1970.14
Group Size (IN): 0.90

I use the Hornady taper crimp, seating to the cannelure (2.080 on the 300 XTP) and crimping to .476. The shorter COAL allows for perfect function from an unmodified pmag 10, which is nice.


First: You should slug your bore. Hard way: get a 45 caliber soft lead bullet. Lube the bore and clamp the barrel in a sturdy barrel vise lash up. Push/Tap the bullet down the barrel with a solid brass rod. Measure with blade micrometer or send it to me. I have a blade micrometer. Easier Way: Load up a slow running 230 FMJ (not TMJ) and fire it into water. Use the slowest burning rifle powder you have (AA3100, RL22, etc) or on the off chance you have Trailboss, use that. Alternately, use a little bit of fast burning pistol powder and grits filler as if you're fire forming brass. I use Unique for fire forming. You only need enough oomph for the bullet to clear the barrel. The reason for slow velocity as you might imagine, is to not have the impact with the water distort it. Measure as in first method.

Next: Measure the outside diameter of one of the reload cases you had to force out of the chamber before you resize it. Using your calipers slide the case through the jaws so that the mouth is even with the farside of the jaw. Mark the nearside of the jaw with a fine mechanical pencil or xacto blade point. slide the case down until the new line is even with the farside jaw and remeasure. mark nearside jaw again. Work you way down the case in jaw width increments until you have measured all the way to the extraction groove. Should yield about 10 or 11 measurements. Repeat with a factory load case that extracted without a problem. Compare the two measurements. If they're different, nothing is amiss with your chamber. Your reloading metrics are off or its just as previously stated, a bad recipe. If they are similar, you may have a tight chamber. Believe me when I tell you! You don't want to have to lap your chamber into SAAMI tolerance. I was so pissed after all that work, I sold the barrel to punish it! (I'm strange, I know) It finally worked fine but every time I looked at it, I remembered the time spent that I will never get back. I'm a patient man, ask anyone I work with. This went beyond human patience and left me bitter. Better off having a competent gunsmith clean up the chamber job with a reamer. Then sell the barrel to punish it! :twisted:

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Re: New rifle eject issues

Postby Texas Sheepdawg » Mon Jan 01, 2018 10:32 pm

Okay. That’s probably the funniest thing I’ve read all night. Hoot getting mad and punishing his barrel. :lol: :lol:
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