How To Convert Para P16 Magazines For Your High Capacity Rock Island 2011 10mm Pistol

In the first post, I outlined the problem that high cap Rock Island Armory 10mm magazines (OEMP164015B) are next to impossible to find right and and shared some of the research I did. I also let the cat out of the bag that I figured out a way to successfully convert Mec-Gar Para P16 magazines (MGP164015B) for use in the RIA pistols.

Safety Comment – Use Dummy Cartridges / Snap Caps

I said this in the first post and it is so important that I want to reinforce the message – I knew I was going to need to do a ton of cycling of rounds. Using live ammo is risky because you have the very real risk of a negligent discharge. To avoid this, order yourself in a bunch of dummy cartridges. There are sellers on eBay that will sell you 10+ at time. Order yourself in 10-20 rounds. You are going to smash the crap out of them due to the heavy recoil spring a 10mm uses. I trashed at least 10-15 of them. Most were due to the bullet being smashed back into the case, one dented the case pretty bad and one deformed the case right at the mouth.

I can’t even guess how many cycles I did – especially starting out. I’m going to hazard a guess and say I averaged about three cycles per dummy before something failed on the dummy as I worked out the kinks and I would load three rounds per magazine to do the testing.

I can’t stress it enough – get dummies to tune your magazines.

Comparing the RIA and Para Mags

Per the first post, Armscor’s RIA mags are actually made my ACT-Mag. Since my pistol did not come with a mag, the seller was able to get Armscor to send me a OEM mag so I had a baseline to compare to. I definitely made sure it function tested properly before doing anything else. Never assume something works until you test it – I can’t stress that enough.

To let you see the differences, here are photos with comments in teh captions of the two mags:.

The RIA model has a plastic baseplate and the the Para model (right) has a steel base plate. Look at the top – the feed lips are much longer on the Para. The magazine locking slot is the same.
RIA on the left – see how the baseplate is stepped. This clears the big mag well funnel on the RIA pistols. The longer flat metal base plate runs right into the funnel and prevents the mag from seating. The RIA model has “40 SW Made in Italy” – the 10mm uses the same mag. Now the Para mag has more marking. On the left edge of the mag in the photo you can see “-A-” and on the right lower-edge in says “MG P16 .40-15”. The followers are a tad different and again the different length feed lips are apparent.
From left to right: Para, RIA, empty Para tube. The RIA follower is slightly different. I found that they work okay but I wasn’t sure at first.
Top is the RIA base plate and the bottom is the Para. The Para’s metal plate is too long but can easily have the front ground down to fit the mag well. The tapered top of the RIA base plate can clear the funnel. The Para’s plate is more like an immediate shelf or duck’s bill that hits the front of the funnel. The other three sides of the Para base plate are fine.

What Needed To Change?

There were two things that needed to change for sure and one maybe:

  1. The feed lips on the Para were too long thus preventing the round from pivoting up to align with the chamber. Fortunately the Para lips need to be trimmed. It would be far harder, if not impossible, to lengthen the lips if they were too short.
  2. The base plate needed to either be trimmed or replaced to fit in the mag well funnel
  3. This was the “maybe”: The followers were slightly different and I didn’t know if the original Para follower would work or not. I figured that I would address the first two points and then decide the next steps. Let’s start with the easy one – what to do with the base plate.

Changing The Base Plate

You have two options here and either one works – it’s up to you. When you remove the Para base plate you will notice that the tube of the magazine’s body rests in a cup. You can remove that front tab off just shy of the depression. I left about a 1/4″ in front. This serves to stop the plate and located it properly on the plate. Seriously – just file, sand, or otherwise cut the extra material off. I used my big 2×72 Esteem grinder to remove the extra material and round the edges.

On the left is a modified base plate and on the right is an original. I reprofiled the plate on my grinder but you could use any tool you are comfortable with. Just remove material until the magazine seats fully. The above modified plate has about a 1/4″ or a tad more of material on it. You just need to leave enough for the plate to be positioned appropriately on the magazine. Yes, the mags do drop free.

The pro of the above is that it is fast, easy and cheap to do. The con is that the bottom of the magazine sits further into the mag well than I would like. You could easily add .100-.200 of material on the bottom using somethign like Kydex or G10 and some quality epoxy or a stiff rubber with an adhesive tape. In all cases be sure to drill or punh the hole out so you can remove the plate in the future – I had that mistake many year ago and learned a lesson – it is way easier to make the hole before you install it and need to remove the baseplate!

Your second option is to buy an aftermarket base plate. I bought some plates from Dawson Precision that I really like. Their +100 plates sit flush with the mag well, the +200 extends just below/outside of the mag well and the +300 sits further yet. All three work and it comes down to preference.

Here are two Dawson extended base plates on the left. The top left is their +300 model and below it is the +200. My modified plate is in the magazine. The Dawson plates are CNC machined and fit perfectly. I like both.

Changing The Feed Lips

This step is slightly more involved than the baseplate. In this step we need to shorten the longer Para feed lips. Again, I was really happy they just needed to be shortened. I was expecting to need to change the angle but shortening them isn’t as bad as you may think.

This is where having an original RIA mag to compare to the Para mag was invaluable. I needed to remove the same amount of material from the front of both feed lips. After watching the pistol load the mag and feed dummy rounds as closely as I could, I decided to use my grinder to remove material in a straight line from the front top edge to where I wanted the new front of the feed lips to be.

Rather than measure and transcribe, I used a steel divider (compass) that was my grandfather’s. I like doing stuff like that when the occasion suits. A divider wants to spring open and a small thumbscrew allows you to adjust the gap between the two points. In the case of the feed lips, I could use it to duplicate the length of the feed lips to each new magazine I needed to cut down using the back of the feed lips as the reference point.

Adjust the divider so the points are at both ends of the RIA magazine’s feed lips. This makes it extremely easy to scribe the mark for where the feed lips will be trimmed to on the Para mags. Yeah, these dividers are old. They belonged to my grandfather, then my dad and now me. Using tools reminds me of projects with my dad and the importance of family.

I would then use a scribe with a carbide tip to etch the distance and a small steel rule served as a straight edge from which I scribed a line at an angle from the front top edge of the magazine tube back to the length I just scribed.

Two things – first you can see the line I will grind down to marked on the magazine body. Second, the scribe has a carbide tip that cuts right through the finish and makes a real easy line to see. The first scribe I tried had a hardened steel tip and it didn’t make a very clear line. The carbide tipped one bit right in and easily scored the finish. Get a carbide tipped scribe if you can. I tried varying the angle it didn’t seem to make a big difference. I tried to more closely follow the original edge of the magazine with latter magazines.

Everything above that line needed to be removed. Again, I used my big 2×72 belt sander, or “grinder” as knife makers call them. I squared my work table to the belt, used a 80 grit belt and removed the offending steel by carefully pushing my scribed line towards the belt in a parallel manner. In English, I sanded off the metal above the scribed line 😉 Any kind of sander would make short work of this but it will be way easier if it has a flat table that will enable to you feed the magazine towards the sanding belt or sanding disc in a controlled manner. I would not do it free hand – same goes with a file but I’ve also seen guys wield a pile of files to do work I only thought could be done by a mill so to each their own. By the way, take care not to overheat the lips when sanding.

This is my 2×72 Esteem grinder (belt sander) and it’s simply wicked. I bought it after my dad passed away and it whipped the extra material of the mags with speed and ease. Because the work platform is trued to the belt’s backing plate, I found I could trim the mags in one pass by putting the flat edge on the platform and feeding the magazine into the belt to remove material. I think it’s an 80-ish grit belt and it left a burred edge that definitely needed cleaning up. Note, these big grinders run cool due to the long belt and a variable speed drive that let’s me dial down the speed so I don’t burn the metal. You don’t want to hurt the heat treat so an easy gauge for novices is to not let your work piece get hotter than you can touch. You can let it air cool or have a dunk tank – just be sure to spray it with WD40 later to displace the water.

Slow down removing material as you get close to the line. Double check all of your measures and scribed lines. It is way easier to take more metal off than to remove too much.

With the coarse cut made, you need to go in and remove all of the burrs and round the sharp steel edges over. I used a specialty flap sander known as a “sanding mop” at 180 grit and then a rubber polishing cone in my Dremel.

I used a type of flap sander known as a sanding mop to do the initial deburring but you could use small files, stones, or whatever you are comfortable with. Here, I am using a rubber polishing bit to clean things up and ensure there are rounded edges on all of the newly trimmed steel.

Last, blow out the tub, wipe it out and clean the body too. You don’t want abrasive materials jamming up the magazine or the pistol. After that, reassemble the magazine and check the action of the follower and that everything seems ok.

After blowing out the tubes. I used a purpose built Arredondo HiCap Mag Brush to ensure the insides of the tubes were clean.

Las step was to function test the magazine with at least three dummy rounds. Four would be even better because you will test feed from both directions as the follower pushes the rounds up from the bottom of the magazine.

Feed Lip Measures

I measured the first few magazines I converted and they were fine so I stopped checking every mag unless I ran into a problem during function testing.

Feed LipRIA MagMGP164015BModified
Front Gap0.356″0.354″0.362-0.364″
Back Gap0.340″0.364″0.336-0.370″
Measures are approximates. I had one RIA mag and measured two MGP164015B mags and averaged the measures. The length was a challenge as I had to make a judgement call as to where the actual front part of the lip was at given the angle. The length was measured from the back forward. I measured three modified mags after fine tuning. Each mag was tuned until it reliably fed.

Fine Tuning

Trimming the lips gets you in the ballpark but more work needs to be done. Every magazine was deburred and had all top surfaces deburred and polished. The inside of the magazine was treated with Dupont Teflon. The feed lips were adjusted until four rounds fed reliably into my RIA 52009 10mm pistol. The final round was tested four times.

To tune the feed lips, use snap ring pliers or chandelier chain pliers to open the feed lips ever so slightly and test. In general, it does not take much. Your goal is to get the bullet pointed towards the chamber as much as possible. Go slow and test – it really does not take much to spread the lips and change the angle.

This fine tuning gets you in the ballpark – you then need to actually go to the range and shoot them to see if any final tuning is needed and then brings us up to the last topic – you need to number your mags so you can keep track of what mags are having problems so you can work on them.

Note: I purposefully fit the mags to use the supplied Mec-Gar followers that can lock the slide open. There are aftermarket Arredondo followers that are really nice and are angled to point the round more at the chamber. The downside is that they don’t lock the slide open – while a person in competition doesn’t need that, I do like to know when I fired the last round.

Click here to go to the section of our online store that has all of our current 1911/2011 magazines and related products.

Number Your Mags

A lot of feeding problems are actually caused by the magazine – notably the feed angle and that is controlled by the feed lips and the follower. The feed lips can get bent when they are dropped, sat on, or whatever. The follower is plastic and will wear over time – not fast, but it will wear.

You need to put a unique number on each magazine so you can track the ones that are having problems and need some tweaking. I’ve seen guys use engravers, paint pins and stickers. What you use is up to you. I’m currently using waterproof stickers on my mags.

I am using waterproof stickers to track my mags. You could use an engraver or paint pen. I find that permanent markers rub off way to easy. The paint pens are a bit better. The method that holds up best is an engraver if you are good enough at it.


I now have my original RIA magazines and a nice back up selection of mags for hunting, going to the range, bear protection, etc. How did they turn out? So far, so good at the bench. I expect most will do really well at the range as well and I am waiting for a chance to go.

Left is the original RIA mag, in the middle is a converted mag with a Dawson +200 base plate and the mag on the right is also a converted unit but with a +300 base plate.
This is the mag well on the high cap pistols. It’s big and I really like it but it really does mean that you need to have a longer baseplate and just a piece of metal like the Para P16 originally had. You can make your own by adding something to the Para plate or buy an extended plate such as the ones from Dawson Precision that I use.
Pistol with the original RIA mag fully inserted. It is almost flush with the bottom of the mag well.
This is the +200 Dawson base plate. It stick out far enough that I can firmly seat / smack / beat the mag into place if I need to. Not much to grab onto though but all of the mags easily drop free – at least during bench testing they do.
The .300 base plat stick out a tad further. Dawson’s number is the length in tenths of an inch – 0.100, 0.200 and 0.300. I ordered some 0.100 plates but they haven’t arrived yet. They will likely be very close to the polymer plate that RIA has on their mags.

I figure there must be guys like me who have one of the RIA high cap .40 or 10mm pistols who want spare mags and hope this will help them out.

After I worked out the process, I converted a bunch of mags for useClick here to go to the section of our online store that has all of our current 1911/2011 magazines and related products.

6/29/2021 Update: Folks, I have converted a ton of mags now so if you order, I want you to know I have the process working smoothly. My biggest problem right now is finding mags – everyone and their brother is sold out of mags – it’s crazy.

4/1/2021 Update: Added dimensions for the modified mags and info on fine tuning.

3/22/2021 Update: I took them to the range and they worked great with both Ammo Inc 180gr TMC ammo and a variety of Underwood HPs.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

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PSA Has 10mm Range and Hollow Point Ammo In Stock!

FYI: Palmetto State Armory (PSA) has a fair amount of 10mm ammo in stock. The Ammo Inc brand 1q0mm ammo is getting good reviews. Click here or on the photo.