I've done a fair amount of research on Showalter and the 4th... I know that Magruder was unhappy that Baird was taking so long to recruit his men. The 4th was first organized in March 1863 and by May, two companies had been created by Showalter and his fellow Fort Yuma defector, T. A. Wilson... but Baird wasn't able to recruit men to fill a third company until July.

The three companies of the 4th were camped near San Antonio in an area they dubbed “Camp Mariposa” – after Showalter’s native Mariposa County in California. “We are constantly getting men,” Showalter wrote to District Headquarters on 11 July, “refugees from California & Arizona who are destitute of means, having lost everything they had in making the trip overland from that country. Our Assistant Quartermaster has no funds for the purchase of horses." But he made no mention of arms.

A few days later, Baird received orders to send Company C (Capt. Conway) to Major Dickinson at District Headquarters for special service and have Showalter & Wilson take Companies A (Capt. Wilson) and B (Capt. Rather) on a recruiting patrol to Bonham, TX. Upon their return from northern Texas about three weeks later, Showalter’s men brought unfortunate news that there appeared to be no men left to recruit in the upper counties. Capt. William S. Rather of Company B suggested that recruiting operations be moved to Austin because that was “the best point for recruiting purposes" (as reported by Baird to HQ on 6 August).

By the end of August, Baird had scraped together four companies and two others had been transferred in from other areas. With the permission of his commanding officer, Capt. Edmund P. Turner, Baird then relocated his men to Austin in hopes in finding more men to fill their ranks.

By 1 September, Confederate commanders were organizing their troops to fight threatened invasions from four different locations—Indian Territory, Arkansas and two from Louisiana (Series I, V26, p198). The threats to the north soon appeared to be most immediate so Brigadier-General Smith Bankhead was ordered to rendezvous in Houston with all available cavalry companies to prepare for a mission to defend the northern border. Unfortunately, out of the more than 1,200 men ready to fight from the San Antonio area, most of them, including all of Showalter’s men, had no weapons. So, Bankhead was forced to leave them behind (cited from the 23 August letter that you mentioned).

Showalter wasn't armed and ready for the fight until late November, when he finally took three companies to the north.

I haven't found any indication from the letters of Baird or his senior staff that they had any specific concerns over Texas-made guns.

Don