AR 15 light primer hits. why?
08-08-2010, 06:59 PM
#1
Nontypical Buck
Thread Starter
Join Date: Oct 2008
Location: Orange county, NY
Posts: 2,949
AR 15 light primer hits. why?
My handloads didnt give me much trouble last time. I was shooting factory federal ammo today, and 10 out of 50 rounds wouldnt go off, a few went off when I loaded them in the gun again, a few didnt. The gun was cleaned and lubed after I shot it last, a few weeks ago. Im new to ARs, whats the usual reason for this? Thanks.
08-09-2010, 05:40 AM
#3
Nontypical Buck
Join Date: Feb 2003
Location: Elizabeth Colo. USA
Posts: 4,413
When you say that your handloads "didn't give me much trouble", I assume that you hand some handloads that also failed to fire? If so, then it is a gun problem, not ammo. problem for sure. If you've cleaned the gun well enough to know that's not the problem, then it comes to springs needing replaced, IMO.
08-09-2010, 10:28 AM
#5
Nontypical Buck
Join Date: Oct 2009
Location: Kansas
Posts: 3,904
You didn't actually SAY whether the primer strikes were light or not, i.e. the pin impressions were shallow in the primers. You described the gun condition well, but you didn't really hit on the measurable aspects to help diagnose the problem, so here's how I'd troubleshoot your problem.
In the event of multiple miss-fires, I check things out in this order:
Ammo:
Shallow pin strikes?
Military spec primers?
Deep set primers?
If the pin strikes are strong, then it's likely an ammo problem. Is it happening with ONE "lot" of ammo, or a certain brand or is it happening with several different brands/lots of ammo? If your gun doesn't like that brand, then pick something else, if it doesn't like a certain LOT of ammo (common lot number), then contact the ammo manufacturer.
Military spec primers are pretty hard to pop, so they may not fire even if the pin impression is deep. If the pin impressions are light, then are the primer's set too deep? The primer should be flush with the bottom of the case, but if they're set too deep, then even a perfectly spec'd pin can't always crush the primer.
If the primer strikes are shallow, and it's failing with ALL types of ammo, then move onto your gun:
Firing pin broken? Peened? Too short?
Firing pin burred? Pin channel burred?
Powder build up in pin housing?
Hammer burred? Hammer path burred?
There are a dozen things that I would look at before I blamed the hammer spring. If your pin impressions are shallow, then remove your bolt and press the pin into it's fully forward position. Is it strongly protruding from the bolt face? If not, then remove the pin and mic the pin. If the pin is on spec, then look to the pin housing. Is there powder build up present? If so, then clean your housing. If not, then the housing hasn't been milled properly (rare but it happens).
If the pin protrusion is strong, then check your pin travel. If the pin or the housing is burred, then the pin will hang. Hone any burrs on the pin or housing. Also, check the overall length of the firing pin. If the rear of the pin is broken, or improperly machined, then the hammer won't be able to drive it far enough forward to crush the primer. This can happen even if the firing pin protrusion is strong.
If NONE of the above are the problem, then check the hammer and the path of the hammer for burrs. If the hammer is hanging while it falls, then it can't strike with enough force to ignite the primers.
The hammer spring would honestly surprise me. Check to see if it's broken or binding. Make sure the hammer travel is free and full, then try a new hammer spring.
Also check the rifle chamber and receiver for build up. If the chamber is fouled, the cartridge may not seat COMPLETELY into the chamber, but may not push the bolt far enough out of battery to defeat the safeties, however, the slight change in position of the bolt can prevent the hammer from reaching the end of it's travel, limiting the firing pin travel. Powder build up in the receiver can also prevent the bolt from closing into battery as well.
In the event of multiple miss-fires, I check things out in this order:
Ammo:
Shallow pin strikes?
Military spec primers?
Deep set primers?
If the pin strikes are strong, then it's likely an ammo problem. Is it happening with ONE "lot" of ammo, or a certain brand or is it happening with several different brands/lots of ammo? If your gun doesn't like that brand, then pick something else, if it doesn't like a certain LOT of ammo (common lot number), then contact the ammo manufacturer.
Military spec primers are pretty hard to pop, so they may not fire even if the pin impression is deep. If the pin impressions are light, then are the primer's set too deep? The primer should be flush with the bottom of the case, but if they're set too deep, then even a perfectly spec'd pin can't always crush the primer.
If the primer strikes are shallow, and it's failing with ALL types of ammo, then move onto your gun:
Firing pin broken? Peened? Too short?
Firing pin burred? Pin channel burred?
Powder build up in pin housing?
Hammer burred? Hammer path burred?
There are a dozen things that I would look at before I blamed the hammer spring. If your pin impressions are shallow, then remove your bolt and press the pin into it's fully forward position. Is it strongly protruding from the bolt face? If not, then remove the pin and mic the pin. If the pin is on spec, then look to the pin housing. Is there powder build up present? If so, then clean your housing. If not, then the housing hasn't been milled properly (rare but it happens).
If the pin protrusion is strong, then check your pin travel. If the pin or the housing is burred, then the pin will hang. Hone any burrs on the pin or housing. Also, check the overall length of the firing pin. If the rear of the pin is broken, or improperly machined, then the hammer won't be able to drive it far enough forward to crush the primer. This can happen even if the firing pin protrusion is strong.
If NONE of the above are the problem, then check the hammer and the path of the hammer for burrs. If the hammer is hanging while it falls, then it can't strike with enough force to ignite the primers.
The hammer spring would honestly surprise me. Check to see if it's broken or binding. Make sure the hammer travel is free and full, then try a new hammer spring.
Also check the rifle chamber and receiver for build up. If the chamber is fouled, the cartridge may not seat COMPLETELY into the chamber, but may not push the bolt far enough out of battery to defeat the safeties, however, the slight change in position of the bolt can prevent the hammer from reaching the end of it's travel, limiting the firing pin travel. Powder build up in the receiver can also prevent the bolt from closing into battery as well.
