Does or did Feferal make a 220gr Gold Medal Match or is this Mk248mod1?

[sht4brnz]

I recently purchased some loose ammo that was claimed to be 220gr GMM. I searched around and have found nothing that Federal has ever make such a round, except for the mk248 mod1.

I do not reload and do not have a bullet puller to measure the weight of the bullet and powder. I feel confident that these are not reloads, as the primers have the same bluish lacquer stain around the primer as the other GMM rounds I have. If there's a better way to identify a reloaded round, please educate me.

If it comes to the consensus that these are the Mk248mod1 rounds, I have read posts warning that these rounds are hot and could cause damage if the barrel wasn't designed for these rounds. So, will a Rock barrel endure these pressures? I am doing my best at reading through and educating myself on what to look for in regards to over pressure indicators but if the brass looks fine after being fired, does that mean that my chamber is in good health?

Below are some pictures of some rounds for comparison. Left to right: the tall one is what's in question, Federal GMM 190gr, Hornady 195gr, Hornady 178gr.




The left head stamp is the tall one, the right is the GMM 190gr.

 

[FCS]

Could be either M248 Mod0 (190 SMK) or Mod1 (220 SMK), both have same OAL and ogive profile is pretty similar between 190 and 220 SMK. FC and year is pretty strong indicator that it is M248.

Chamber dimensions is going to be a large factor in determining peak pressure & if you'll have an issue. How much freebore do you have?

 

[sht4brnz]

I'm not familiar with the term freebore. is it in reference to where the lands begin?

All I can tell you is that there aren't any land marks on the bullet after it's been chambered.

I would have assumed the GMM 190gr would have had a better resemblance of the mod0.

 

[FCS]

Both Mk248 mod0 and mod1 run a longer OAL.

If you do not have rifling marks on bullet after chambering and extracting round, you'll probably be just fine.

Check diameter of fired case just above belt, check for ejector swipe on case head as those will be to two most obvious places excessive pressure will show up.

Freebore / lead are essentially same thing. What is the length of the straight cylinder in front of the case mouth that is approx. 0.001" larger in diameter than bullet? Lead angle would also be a factor but 1.5 degrees is pretty much the standard anymore.