.300 WM Won’t Chamber Factory Ammo

[AK.300]

Morning,

Have gleaned tons of valuable info here over the years, and recently ran into something that made me want to offer up to the collective wisdom as I'm scratching my head bigly.

Bought a Mossberg Patriot in .300WM for my son. Sighted in with a few different factory ammos last year and rifle was actually shooting about 1" groups at 150 yards with 180gr Win Power Point.

Have kept my eyes open for same ammo that shot so well and it's been hard to find, .300wm in general has been pretty scarce. Finally found some and bought two boxes.

Took rifle and two new boxes on coyote hunt last weekend. When got out there (3hr drive..), figured I'd put a couple rounds through it with new box before the hunt. However, bolt handle wouldn't turn down even slightly when chambering first round. Pushed into chamber fine but wouldn't rotate/close. I tried all 40 rounds between the 2 boxes and only 3 would fully chamber and bolt was tiiiight in closing on those. Too bad for 2 out of 3 yotes tho…

Anyway, I'm moving to reloading now, tired of not being able to find ammo and found more time lately so would like to start shooting more than just a few rounds before deer season. If ever shoot factory again, I'll probably chamber every round once before heading out, never occurred to me it'd be a problem…one more thing..

Curious tho, I got home, and the same rifle chambered 3 other boxes of different factory ammo just fine. I then threw a few rounds of the 2 suspect boxes into a savage 116 and I could close the bolt but it took a lot of force and didn't want to get something stuck so only did a couple. So suspected the ammo is bad.

Big head scratcher for me is…Put calipers on a round from the suspect box and could find really no tolerance issues. I compared the values to both another round that chambered just fine in the Mossberg and the case length SAAMI spec (I believe is 2.620-.020) and it was within SAAMI and only a few thou difference between the two rounds, in fact, the suspect round case length was 2.613 and the other was 2.610, total round length was 3.310 for suspect round and the other round that chambered fine was 3.312. Diameters were same between both rounds: shoulder 0.490, base 0.525, neck 0.334. Tried measure neck length from case end to shoulder radius and couldn't see any real differences and got about .260 on both. Couldn't get a good shoulder length measurement from radius to radius on case but using mark1 eyeball, they looked pretty identical. So .003 longer for the suspect round than the control round, but still within 2.62 max.

Anyway, sorry for the novel on first post but as far as I can tell, the shells are nearly the same and within spec, so forgive my ignorance but wondering if there's a rifle issue (could rifle chamber be so tight that .003 longer from control round but still .007 under max causing issue), or bolt issue, or a shell measurement I'm missing, or??

Thanks for any help/opinions/etc.

AK.300

 

[Rick Richard]

Sounds like the shoulder length of the suspect ammo is too long for the chamber. purchase a shoulder measurement tool and verify. You will need it eventually when you start reloading.

 

[Chadp82]

I had a similar issue with a Browning A Bolt years ago.

Had some factory rounds, a little snug, but bolt would at least close.

Since I was a reloader, I sized brass trimmed to SAAMI length and they wouldn't chamber all the way.

I tried a few of the factory versions and they were snug. I made sure everything was thoroughly cleaned etc. still had the same issue. I measured the case for the factory ammo and they were a couple thousandths shorter than SAAMI.

I trimmed a little shorter, and I mean very little, on the sized cases than the SAAMI length and the problem was resolved.

I would maybe try trimming just slightly and see if it helps. It also could be a defect or poor tolerance from the manufacturer in the chamber, but it's unlikely.

Also, as just mentioned, check the shoulder.

I would get the calipers and check the boxed ammo too just to see. Could have been a tolerance off on that lot #.

Start with measuring to see if it's the ammo or not first. Then if needed you can move onto the rifle.

That A Bolt to this day has been my go to hunting rifle for 15+ years. Since it's a 280 REM, I don't commonly see shelf ammo, and I rely on reloading. If it was a more common round, I would have probably done more in the event I needed to buy a box off the shelf.

You could also try higher quality ammo. My issue was with Remington core lokt. Over the years I have used Nosler and Barnes boxed stuff and it functions flawlessly.

 

[entoptics]

Might be tough to measure, but did you check the base to belt distance?

In my experience, virgin 300WM (and all belted mags I've dealt with) is usually WAY short from base to shoulder. They will often be >0.015" short compared to once fired. My 264WM Winchester brass was >0.025" shorter.

The belted mags are technically head spaced off the belt. So if the belt is a few thousands too long, that would cause it not to chamber, even if there was miles of clearance at the shoulder. Would also explain why you can't force it to chamber. Smooshing the shoulder down a few thousands with the bolt handle would be a lot easier than smooshing the belt down even a couple of thousandths.

Regardless, sounds like bad ammo. I'd be contacting the vendor or manufacturer looking to get my coins back, or at least some replacements.

 

[victor3ranger]

Smoke one of those rounds and see where the problem is.
I bet that the shoulder is too far forward or it's at the belt
If you don't want them send them to me

 

[muledeer01]

What type of bullets are they? My brother in laws Browning A bolt needs the Hornady interlock or Berger classic hunters set well back to chamber.

 

[wyosteve]

This post is a good reminder for me. If I'm taking any ammo on a hunt, I usually chamber every round before I leave to make sure they fit. Would really suck if you needed another shot at something and the round wouldn't chamber.

 

[victor3ranger]

This post is a good reminder for me. If I'm taking any ammo on a hunt, I usually chamber every round before I leave to make sure they fit. Would really suck if you needed another shot at something and the round wouldn't chamber.

I chamber every piece of brass before I load it. I have run in to something similar and don't want to go through it again

 

[AK.300]

Good stuff here, thanks.

Will be getting a shoulder measuring tool and will also try to measure the belt with my calipers.

Contacted the mfr and will see what they have to say/do.

Going to start putting together a reloading set-up so will have readily available ammo..and rounds that chamber..

Thanks again.

AK.300

 

[AK.300]

What type of bullets are they? My brother in laws Browning A bolt needs the Hornady interlock or Berger classic hunters set well back to chamber.

Win Power Point in 180gr. They shot great with the first two boxes I ran through it, grouped better than a couple other brands I tried.

 

[sable tireur]

Curious tho, I got home, and the same rifle chambered 3 other boxes of different factory ammo just fine. I then threw a few rounds of the 2 suspect boxes into a savage 116 and I could close the bolt but it took a lot of force and didn't want to get something stuck so only did a couple. So suspected the ammo is bad.

Regardless, sounds like bad ammo. I'd be contacting the vendor or manufacturer looking to get my coins back, or at least some replacements.

This is your answer, because of your first quote above. If all other ammo fits, it's bad ammo.

Contact the manufacturer and get a refund.

I had a similar experience with Winchester ammunition. Called, sent email with pictures and summary. They offered replacement or refund. Very polite and helpful.

Enjoy!

 

[FEENIX]

Morning,

Have gleaned tons of valuable info here over the years, and recently ran into something that made me want to offer up to the collective wisdom as I'm scratching my head bigly.

Bought a Mossberg Patriot in .300WM for my son. Sighted in with a few different factory ammos last year and rifle was actually shooting about 1" groups at 150 yards with 180gr Win Power Point.

Have kept my eyes open for same ammo that shot so well and it's been hard to find, .300wm in general has been pretty scarce. Finally found some and bought two boxes.

Took rifle and two new boxes on coyote hunt last weekend. When got out there (3hr drive..), figured I'd put a couple rounds through it with new box before the hunt. However, bolt handle wouldn't turn down even slightly when chambering first round. Pushed into chamber fine but wouldn't rotate/close. I tried all 40 rounds between the 2 boxes and only 3 would fully chamber and bolt was tiiiight in closing on those. Too bad for 2 out of 3 yotes tho…

Anyway, I'm moving to reloading now, tired of not being able to find ammo and found more time lately so would like to start shooting more than just a few rounds before deer season. If ever shoot factory again, I'll probably chamber every round once before heading out, never occurred to me it'd be a problem…one more thing..

Curious tho, I got home, and the same rifle chambered 3 other boxes of different factory ammo just fine. I then threw a few rounds of the 2 suspect boxes into a savage 116 and I could close the bolt but it took a lot of force and didn't want to get something stuck so only did a couple. So suspected the ammo is bad.

Big head scratcher for me is…Put calipers on a round from the suspect box and could find really no tolerance issues. I compared the values to both another round that chambered just fine in the Mossberg and the case length SAAMI spec (I believe is 2.620-.020) and it was within SAAMI and only a few thou difference between the two rounds, in fact, the suspect round case length was 2.613 and the other was 2.610, total round length was 3.310 for suspect round and the other round that chambered fine was 3.312. Diameters were same between both rounds: shoulder 0.490, base 0.525, neck 0.334. Tried measure neck length from case end to shoulder radius and couldn't see any real differences and got about .260 on both. Couldn't get a good shoulder length measurement from radius to radius on case but using mark1 eyeball, they looked pretty identical. So .003 longer for the suspect round than the control round, but still within 2.62 max.

Anyway, sorry for the novel on first post but as far as I can tell, the shells are nearly the same and within spec, so forgive my ignorance but wondering if there's a rifle issue (could rifle chamber be so tight that .003 longer from control round but still .007 under max causing issue), or bolt issue, or a shell measurement I'm missing, or??

Thanks for any help/opinions/etc.

AK.300

Sorry, but eyeballing can be deceiving. You need actual measurements of the ones that chambered fine vs. those that will not chamber. My best WAG is a lot longer than a .003" difference.

For obvious reasons, the second picture will not chamber. Good luck!

 

[AK.300]

Thanks again for all the thoughts here, want to provide confirmation of what the collective has settled on: ammo issue.

Got the calipers back out on the suspect ammo, along with a box of Federal, Swift, and Corelokt.

Measured 3 rounds from each box-as best as could using calipers. Measured from top of belt to bottom of case at four points around circumference and took average. Then repeated for 2 more rounds and took that average. Repeated that for each mfr for following values:

Rem- .219
Swft- .215
Fed- .218
Win PP- .236

(FWIW, the multiple measurements around circumference and the measurements of multiple rounds from each mfr were all very close, around +\- .001, no huge scatter in these values when took the average).

Dunno what the spec would be for this measurement, and using calipers on top belt radius to bottom of shell edge probably not the most accurate (hence the repeated measurements and averages..), but seems this is the issue.

Thanks again for thoughts here, would've always wondered..

Main take away for me is to be aware of this new gotcha if using factory ammo again and cycle each one before setting out.

Best regards…

AK.300

 

[memtb]

I was gonna suggest checking the OA case length, as possibly too long!

But, Chad covered that early on!

If you have access to a "go - no go" gauge set, you may check the chamber….it may be a bit tight for a round that's on the high side of spec's! memtb